results attained by most of the competitors per mile to build it. A number of other railway It is not necessary to employ a lawyer unless there were so satisfactory as to leave little room projects are seriously entertained, and some of be a dispute about the land. The chief expense for any but microscopic improvements. The them will probably be carried out in a few years. is in going to the Land Office with two witnesses. same principles obtained with all the best Amongst these are the Sancelito and Humboldt At the present time about 86,000,000 acres of makers. Short steam ports, double valves. Bay Railway; the Southern Pacific Railway, from the public land in California are open to occupaseparate cut-off, and steam jackets, combined Gilroy to Fort Mohave; the Beckworth Pass tion. Many of these are too rugged and barren Railway, from Oroville to Ogden; the Vallejo and to pay for cultivation in the present century, exwith every variety of schemes for lagging Stockton Road, to connect these two points; the cept in patches. Of the land available for tillage exposed surfaces, and marvellous examples railway from Santa Cruz to Redwood City; the surveyed and ready for occupation, there are of feed-water heaters, were all to be found. line from Santa Cruz to Gilroy by way of Wat- about 44,000,000 acres, in the Sacramento Basin, In a word, the engines under trial exhibited sonville; the railway from Gilroy to Monterey: the Sierra Nevada, and the Klamath Basin. All that combination of elaborate workmanship and the line from Gilroy to San Diego, along the the land on which it is supposed that grain can with what we may well call highly trained coast. No less than 900 miles of railway have be grown with a profit at present has passed out science which places England at the head of been completed in California within the last five of the control of the government, but the future the nations in this sort of engineering. years. These include 600 of the Central Pacific; profts depend to a great extent upon the means of A word in conclusion about the laws of 125 miles of the Western Pacific; 105 of the transportation, and large districts that are now too trial as established by the Royal Agricultural California Pacific, running from Sacramento and far from market will become valuable when they Society. The pressures of 50lb. for single Marysville to Vallejo; 30 of the Southern Pacific, shall have been made accessible by railroads. and 80lb. for double cylinder engines are, we Oregon; and 20 of the Los Angelos. from San Jose to Milroy; 20 of the California and There are plenty of brokers and others ready to cheat strangers to the country by selling them consider, too low; the foot poundage system of test alone, without taking the work done inferior land considerably above market price, so it is bad policy to buy in a hurry; the purchaser by the boiler, is defective-it does not go by close examination of the land and of the far enough. If the engines only are tried, neighbouring sections and prices paid for them, no boilers should be put under steam; if the should make sure that his bargain is a good one engines are tried in some cases without the before it is closed. boilers, why should the evaporative capabilities of the boilers receive no special atten tion ? An engine and boiler are somewhat like partners in a firm, each with his particular province, and the mutual success of both depends on each being able to command good results in his own department. THE RESOURCES AND RAILWAYS OF California has, according to estimate, 80,000,000 acres of tillable land, of which only 5,000,000 acres are enclosed, and more than 48,000,000 acres remain open to purchase. Much of this land is remarkably fertile, some producing more wheat, more grapes and fruit to the acre than any land in the Atlantic States, or Europe. In the winter, snow and ice are great rarities in the lowlands of California, and the whole country has a climate and atmosphere like Italy; in the southern parts it is very hot in the summer, but not along the middle coast; heavy woollen clothing is worn throughout the year in San Francisco. Fever and ague are found in the lowlands of the Sacramento basin, and the fogs of the middle coast are not good for diseases of the throat and lungs; otherwise the climate of California is conducive to longevity. The farmer needs no barn to shelter his grain, no stable for his cattle; his horses will work, and his cows BY the last mail we received from San Fran- yield milk tolerably well, if they never get any cisco a newspaper of enormous size called "The Weekly Alta California;" the sheet on which it is printed is 4ft. 10in. long, and 3ft. 5in. broad. This large surface of paper, dated May 12, 1870, is almost entirely covered with accounts of the resources and geography of California, and two pages are filled with a prize essay on the subject. In a country like the United Kingdom where there are more paupers, and where the capitalists and great landowners are richer, than in any other nation in the world, all information about desirable fields for emigration is of great interest to the bulk of the people. We therefore proceed to summarise some of the leading facts set forth in the large journal just mentioned. Within the last 80 years 6,500,000 persons have crossed the Atlantic to become permanent residents in the United States, and at a moderate estimate they added each 1,000 dollars to the wealth of the country by simply taking up their homes there, and much more by the labour which they did after their arrival. California being thinly peopled it is better to go there than to one of the States which is thickly populated. The population of Illinois is 2,500,000, and of California only 600,000. An addition of 1,000,000 is only 40 per cent to the former and 166 per cent. to the latter; and the increase in the value of land and in the amount of trade is about in the same proportion. In what has already been stated, a very small fraction of the solid information given in the essay by Mr. John S. Hittell has been summarised. There is a great deal of information in his essay, about the mining districts of California, its manufactures, and the trade of San Francisco. He also gives statistics as to the cost of living and the rates of wages. Wages in California are from 20 to 200 per cent. higher than in New York. At the present time the chief demand in California is for common labourers, farmers, carpenters, miners, blacksmiths, cooks, and boys. Servants who only get about £10 a year in England are eagerly engaged there now at from £4 to £8 per month, as fast as they offer themselves. It is much easier to cultivated food. There is a great opening for get employment in rough or mechanical work manufactures, because of the abundance of raw than in clerking or keeping books, and those who material, and the distance of the country from the have no money and no friends in California able present great manufacturing centres of industry. to assist them, and no speci 1 knowledge that will The richest mines of the northern hemisphere are certainly command employment, should not go in California. The annual production of gold is to California expecting an easy life. Men who exmore than 20,000,000 dollars. There are also valuable pect to make their living by the shovel, the plough, mines of quicksilver, tin, copper, coal, manganese. table of the rates of wages paid to men of different and the axe, are wanted. Mr. Hittell gives a long and beds of marble, slate, sulphur, porcelain-clay, soapstone, and asphaltum. In the foot hills of the trades, in the month of May last. Mechanics who Sierra Nevada millions of acres contain gold work by the day get from 3 to 6 dollars per day in quantities sufficient to pay well at some future in gold, which in English money is from 12s. 6d. day. At present, there are many farmers who to 25s. per day. The charge for board and lodgsluice out the ravines on their farms with profit ing in San Francisco for poor people is from £4 to in the intervals of agricultural labour. The £8 per month, and for those who can afford to live country has some drawbacks. There is an comfortably from £8 to £15 per month. The cost of occasional drought (about once in seven years on living is greater in California than in any other an average); when there are more trees and more country, but it is not so great as in most other cultivation, it is hoped that there will be more countries when compared with the rates of wages rain, and it is probable that canals for irrigation and general profits of business. will at some future time be introduced. This latter point well merits the attention of engineers. The high wages and rates of interest, which are double those in the eastern States, are disadvantages to some classes, but they are very advantageous to others. The news has just reached London from New and that thousands of farm labourers are thereby York that this year is one of drought in California, thrown out of employment. These droughts, as years. Here, then, is an opening for engineers already stated, occur on an average once in seven and capitalists to carry out schemes whereby the The public land of the United States is all sur- richly productive soil in the lowlands may be irriveyed or unsurveyed. All, unless specially re-gated with water from the lakes in the mountains. served, is open to settlement and occupation by Many railroads will soon be built in California. any citizen or white man who has declared his The road from Stockton to Visalia, a distance of intention of becoming a citizen. All the public 160 miles, will run through the richest grain dis- lands are disposed of by sale at auction, private trict of the State, a large part of it now unculti-entry, pre-emption, and homestead claim. After vated, because there is no mode of transporting land is surveyed into sections it is advertised for produce to market at any expense which the THE WORKMEN'S INTERNATIONAL EXHIBITION. sale, and all that is not occupied by pre-empters Ahibition is not on such an extensive scale as farmers can afford to pay. The Oregon and Cali- or homesteaders who have filed notices of their LTHOUGH the Workmen's International Exmany other exhibitions that have been organised at home and abroad in recent years, it is an undertaking of sufficient magnitude to entitle the committee of management to liberal indulgence in the matter of its incomplete and unfinished state at the opening. It is not as yet-with many of the foreign contributions promised not to hand and with some of the contributions received not yet placed-in a condition to admit of systematic notices, and a general sketch, with only a few particular references, is all that can at present be attempted. It may be supposed that the Workmen's International Exhibition is, in a sense, the rehearsal of acres or less in legal subdivisions. The applicant a section of the greater exhibition of the coming goes upon the land, files his application, builds a year. Rehearsals doubtless serve useful purposes, house, and cultivates the land for five years; files and we can only hope, in relation to this exhibian affidavit sustained by two witnesses of continuous tion, and any others that may be held during the residence and cultivation, and then gets his patent current year, that they may not absorb or dissipate on payment of 22 dollars fees if he have 160 acres, the spirit and zeal necessary to the organization, or 11 dollars if he have 80 acres. The affidavits completeness, and success of the more important are all taken by the land officers without charge. I display which is to follow. This observation is suggested not solely by the holding of this Agricultural Hall Exhibition, but by the symptoms apparent elsewhere of a disposition to engage in a kind of "little goes " that may detract, we fear, from the vigour and success of the first of the international exhibitions to be opened in 1871. A proposal is made, we notice, at Edinburgh, to have in the coming autumn an Exhibition of Works of Art and Skill. These smaller local exhibitions are doubtless meritorious in aim, and may be useful in result, always provided that they do not hinder concentration and zeal in the collection, arrangement, and display of objects at the more truly international exhibition of next year. We last week referred to the large number and high character of the contributions from Italy and by Italians. This department is certain to prove one of the most attractive in the exhibition, including as it does the exquisite mosaic work of Salviati, and other examples from Florence; the fine majolica ware of Cat in 5 hours and 15 minutes. If he had taken as In the same neglected corner some curious Notes we made concerning other exhibits must be reserved for a future number; we were glad to take the impression from the Exhibition on its opening day that it deserves, and will, we hope, command success. NOTES BY QUIDNUNC. hammering rainfall as that which accompanied the thunderstorm of Tuesday morning last. In some fields small forces of women and children might have been seen at work making very slow progress upon ripe fields that the machine mower would have cut down, as they ought to have been, in a single day. Surely the method of the farmers in the Lothians, the Carse of Gowrie, and the best farming districts in Scotland, of cutting their cereal crops sharp before they are fully ripe, is better than the dead-ripe system of the south. The extraordinary weather we are having renders rapidity in harvesting operations of vital importance. We have not only high temperature, but an almost unprecedented degree of aridity in the air, the hygrometer giving indications seldom before known. On Friday last we found the thermometer at the Radcliffe Observatory, Oxford, indicating 90-6 in the shade. On the 24th, at Clifton, it was at 91-3deg., where it has only grow in popularity. He is not to be permitted 89.7deg., and the wet bulb 63-8deg., complete THE Chief Commissioner of Works does not dry bulb of the hygrometer at 3 p.m. indicated reached 90deg. twice in the last 18 years. The to perpetrate the absurdity of leaving the mud-saturation being, of course, represented by 100, bank of partially desiccated sewage precipitation a margin truly extraordinary, the difference bein the bottom of the Serpentine, but he will not tween the two bulbs being often as low as from consent to reduce the water to a safe depth. On three to six degrees. The readings on three days Monday evening last the Chief Commissioner was were-dry 88-Ideg., wet 66.2deg.; 87-8deg. and required to vindicate and explain in the Commons 65-7deg.; and 83-7deg. and 69-1deg. respectively. a vote for £10,170 for new buildings and alterations Whether attributable or not to the extraordinary Mr. C. Bentinck, in the Houses of Parliament. Mr. B. Cochrane, Mr. Cowper-Temple, Lord John temperature, we cannot say, but the_wonderful phenomenon of the Mirage was on Friday last Manners, Mr. Gregory, Colonel W. Patten, and witnessed at the mouth of the Firth of Forth. Mr. Beresford Hope (high names) all condemned The Bass rock and the Isle of May presented the the proposal, and concurred in deprecating the most wonderful phantasmagoric appearances. Chief Commissioner's treatment of Mr. Barry Ships and boats appeared sometimes double, somewhose plans and suggestions he had adopted times in triplicate one in the water, and another, without acknowledgment, and which he was about to alter only to spoil by the provision of a "tavern inverted, in the air, with the third between them in an angular position. Whatever may have been fine examples of carved and inlaid bar" in the corridor and otherwise. The moral of the cause of the Mirage, the hot, dry weather, and verb, "Let the shoemaker stick to his last," the speeches seemed inspired by the homely pro- the uncertainty of its continuance, is an admoni talani; the beautiful inlaid work, and the wood carving, sculpture, and other examples of art and skill. The contributions from Bombay, in "Black wood" furniture, very richly carved, are also exceedingly fine, and, in the same locality, the beautiful specimens of glass manufacture by George Lowe, of Birmingham. The exhibits from the Ventnor Glassworks also arrest the attention and command the admiration of the visitors. The condition imposed by the council that the names of workmen and inventors should be attached to the exhibits is not in all cases attended to, but there is a sufficient number of instances of conformity to the rule to furnish materials for comment, and, amongst them, the fine examples of spiral, oval, and other ornamental turning by Mr. F. Golley, of Bolsover-street, Portland-road, London. In the furniture class there are also many work by London workmen, who figure very creditably in addition in Class 4, Decorative art, leave architecture to architects, and law to law./tion to the farmers to cut and garner their ripe missioner, but what recked he? He had the trampled under the hoofs of war horses, and we on the Continent may be, in many instances, yers. The speeches were against the Chief Com-corn with all expedition. The unreaped corn-fields votes, and the £10.170 will be spent under his shall certainly need all that can be gathered this direction instead of that of Mr. Barry. It would in which there are numerous excellent specimens woods, with floral and geometrical designs for of graining and imitations of marbles and fancy decoration. On the machinery side of the hall we were glad be well if the strong government were defeated year as much as ever we did. Investments in to notice one among many veritable working men displaying with pardonable pride the product of his own inventive brain, and the result of his own patient thought and toil-we refer to the standing bench of Mr. H. Lewis, for enabling shoemakers to stand during all parts of the process of making hand-sewn, pegged, or riveted boots, also for lasting and finishing every description of machine sewn work in a standing position. The apparatus is wonderfully compact, and a very complete and ingenious piece of mechanism, and marvellously low in price. The inventor claims for it that it effects a saving of 25 per cent. in time, that a child's No. 1 or a man's No. 14 can be fitted in it with equal facility in a few seconds, that all kinds of lasts, wood or iron, can be fixed in it, and that it can itself be fitted to a table in a few minutes, that it economises space, and that it can be worked at once by any man of ordinary intelligence. Among the striking curiosities of the Exhibition oftener than it is. that blows nobody good." So a number of men prize mowing and reaping machines are well and such a scene has not been witnessed since 7.50. their fittings and stores ready. NOTES ON RECENT DISCOVERIES IN PREVENT THE M. BAZIN has made a curious discovery, which merits the attention of photographers. the time of the Crimean war. At Chatham Royal we noticed a cement of extraordinary tenacity, the and miners are directly dependent for employ- scores of fields of wheat and barley standing un- We may dismiss in a few words one more mode of preventing the incrustation of steam boilers. It consists in putting some horn shavings in the boilers. These will, of course, by long boiling, give a weak solution of gelatine, which will, no doubt, suspend the particles of carbonate of lime and prevent them from forming a coherent layer. Spongy gold is used by dentists for stopping teeth. The mode of obtaining gold in this state has been kept a secret, and we have been told that all used in this country is imported from America. We read in a German journal that it may be prepared by adding to a solution of one equivalent of sesqui-chloride of gold one equivalent of bicarbonate of soda, and then boiling with four equivalents of oxalic acid. The gold is said in this way to be precipitated in the spongy form desired. Coloured basket work is largely manufactured in and exported from Berlin. There is nothing particular in the manufacture, but Böttger devotes an article in his "Polytechnic Journal to a description of the modes of dyeing and varnishing the wood employed. The finest willow rods are used, and these are either dyed first by boiling them with the usual dye woods and then the manufactured articles are sized and varnished, or the basket work of white wood is sized and varnished with coloured varnishes. The varnish employed is said to be a simple solution of sandarach in spirit scented with oil of lavender, and coloured as may be required. AERONAUTICAL SOCIETY. AT the last meeting of the above society, after the reading of Mr. Sénécal's paper on "An Instrument for Measuring the Flight of Birds " (which we gave at length on pp. 61 and 62 of last week's MECHANICS' MAGAZINE), Mr. Moy remarked that the author was deserving of great credit for his ingenuity. He had done more than any Englishman could do, and was deserving of their warmest thanks. Mr. Sénécal handed round minute models constructed to imitate the flight of insects. He said that he was constructing an apparatus to measure the pressure of the air against the wings of birds. He hoped on a future occasion to show a small watch which he had made. It was not as heavy as a threepenny piece, and would go twenty-four hours. He did not believe the weight would be 3 dwts. From this construction of watch he had drawn an apparatus for fixing on the wing. It was self-registering, and could be made to register the pressure of the air and the angle of the wing for five or six minutes. A Member remarked that it was important that they should make experiments to show the number of strokes and the given resistance to raise a certain weight. The Chairman, examining Mr. Sénécal's mechanism, remarked that it had a lever escapement of extreme delicacy. Mr. A. Stewart Harrison then read a paper "Upon the Work and Constitution of the Committee for Administering the Experimental Fund of the Aeronautical Society." He said that the first point to be ascertained was what portion of the weight of the human body could be air borne by aeroplanes of various forms and number, set at various angles passing with greater or less rapidity through the air. In other words, the simple relation of velocity to the sustaining power of the air This being determined in any practicable way' such, for instance as that suggested by him at the last meeting, the next question would naturally be, How is the balance of weight to be taken up? This we might term the "wing question; the other might be called the "tail" question. He was of the same opinion as that expressed in "Once a Week" some few years ago that continuous circular motion was the true key to its solution. The paddle and the screw of steam vessels afforded arguments in that direction to the abandonment of all flapping schemes whatever, and he was of opinion that until all these questions were settled no attention should be paid to any other motive power than that derived from the human muscles. The remainder of his paper was devoted to the constitution of the committee and the advantage which would accrue to humanity by a successful issue to the labours of the society. Mr. Chalon read the following paper descriptive of his aerial machine : In submitting to your notice the plans and description of the aerial machine I have now the honour to introduce it is, of course, needless to say a word to those so well informed as the members of this association on the subject of the various proposals hitherto made with regard to such con trivances. The novelty in this, which it is believed will be found to be one of a practical character, is the mode of propelling the wings. The position of the points of attachment to the car is in the above engravings shown as at the centre of gravity of the machine, but it will be seen that provision is made for varying this position as the result of experiment may indicate, as it is believed that a position in advance of the centre of gravity will be found to be the best. The form and size of the wings and of the parachute are also open to modification. A is the airproof umbrella roof or parachute formed of the lightest and toughest material, the exact dimensions to be decided upon by experiment, but (say) 10ft.diameter. B is the car or standing place for the aeronaut, supported by the (rigid) continuation of four of the ribs of the roof or parachute. CC are the two wings, say 10ft. long, each formed of expanding ribs covered with similar material to the roof, one attached to each side of the upper part of the car affixed by movable slides and belts, so that their position may, as before remarked, be varied if necessary, and working independently of each other, either on a swivel or ball and socket joint, so as to enable the aeronaut when expedient to work either one separately, and at any angle of inclination required. DD (and these constitute special features in the arrangement) are two powerful india-rubber ropes springing from the outside of the bottom of the car and diverging to each rib of the wings by strong catgut, capable by their elasticity of stretching according to the force applied. EE are strong cords terminating similarly in catgut attachments at points on the ribs of the wings to meet D D, passing over rollers at either side of the roof or parachute, the other ends coming into the hands of the aeronaut, who by simply throwing his weight on to them will raise the wings at pleasure, according to the force exerted, thus stretching the india-rubber ropes beneath, whilst the sudden or gradual relaxation of such pressure on the part of the aeronaut will occasion the outspread wings to strike the air with a force equal to the strength of the india-rubber ropes. This is anticipated to be far more than sufficient to enable a man of ten or eleven stone weight to navigate the air. Should it be found expedient or necessary to increase the rapidity of action of the wings beyond that attainable in this direct and simple way, the object can be attained by the use of a multiplying wheel attached to the It is submitted that the umbrella roof will take off one-half the weight of the aeronaut in descending or in floating in the air, whilst the peculiar principle of the wings will enable him to imitate exactly the action of a bird in flight. In conclusion, it may be stated that the plan now proposed is simple, capable of being cheaply experimented upon and improved, easily and safely tried from a small elevation, and worthy the attention therefore of your society, and the inventor respectfully invites the co-operation of the association or of any of its members in carrying the proposal into practical effect. In reply to Mr. Moy, was 281b. Mr. Chalon said the weight of his apparatus and weighs 30lb. The next paper, by Mr. Quartermaine, "On the Angle of Impact of the Air on Surface," was taken as read, owing to the lateness of the hour. It was as follows: this science. lines E E, or by other simple contrivances well-convexity. The wings of flying animals fulfil wing surface than the bird. This shows the importknown to mechanicians. both these conditions. They can also readily ance of surface, and on that depends their relative obtain the angle of inclination developed in the weights and requisite velocity. In order to meet pitch of screw propellers. The necessity of this the various requirements of flying animals this provision often occurs in their flights, but with condition of relative weights to surface in air the aeronaut would only be required at the ter- is by velocity indefinitely modified, and the presminus of his journey. The necessity of feathering sure or force of its repellent property developed exist. It may be well to inquire, How can this at our meetings that the heaviest birds have the the propeller in every upstroke does not therefore proportionately. It has frequently been observed action be obtained when necessary? We have smallest wings, and that there appears no correalready seen that the most effective resistance to sponding proportion between weight and surface a concave surface is obtainable when advancing in the heaviest and lightest animals. This seemupon air at right angles, i.e., at right angles to ing discrepancy disappears when we unite weight to body in motion. If, then, the stroke of sur- quantities we find the most exact ratio to exist, stroke of surface, not necessarily at right angles and surface with velocity. By the unity of these face be made at right angles to the horizontal and throughout all operations the expenditure of effect will produce an upward and onward motion; is precisely the same in producing equal results, or perpendicular direction of body, the resultant force in overpowering the constant force of gravity but if the stroke be made at an obtuse angle-or whether the expenditure be in the actions of the as with a screw blade of sharp pitch--its descent diver, the albatros, or the butterfly. If we have would be instantaneous, as when a bird of prey great weight and small surface we must have high ponnces on its victim. In the bird, then, this velocity, as in the sparrow; but if small weight of wing surface so as sharply to incline upwards in butterflies. The simple problem of weight to action is obtained by turning the anterior margin and great surface, then low velocity will suffice, as its posterior margin, and thus allow its point of surface and velocity admits, then, of most exact impact on air to become divergent, as from a con- adjustment by the rule of proportion, for by mulThe inquiry into the most effective angle atriage this action must be obtained independent of pressure or weight of air, and dividing the provex surface or incline plane. In the aerial car- tiplying the wing surface by the atmospheric which aeroplanes or wing-surfaces should be fixed the engine if required. The form of the propelling duct by the weight of the body to be raised we is an important and gratifying feature in the de-surface and its angle of impact on air becomes, obtain the comparative weight between the air velopment of aeronautical science, Students ap- therefore, a matter of the highest importance in and body extended over such surface. It only reproaching this division of physical science for the first time soon discover that the air possesses promains to ascertain what velocity must such surperties in common with all matter, and also pro- obtained from velocipede motion would be other equal to or slightly exceeding the weight of body The suggestion to press into this science data face acquire to obtain from the air a resistance perties uncommon to other matter. One is weight, than serviceable. If on a velocipede a man could actuating that surface. The value of velocity has and is simply due to the influence exerted by the attain a speed of ten miles an hour, when in his always proved the most difficult in this science to earth's inherent attractive force or gravity. Another is elasticity, and this is simply due to the great pre- the least amount of resisting surface to forward point is now felt to be all-important. The manner most compact and dense capacity-i.e., exposing determine, and the want of reliable data on this ponderance of the repellent force inherent there-motion-if he increases his surface for lightening in which the surface is to be opposed to the air in; whereby, although it permits the air to be his load on land (say) to the extent of only 10 will evidently affect the result. For example, we compressed under weight or action, that force square feet, and obtained therefrom an ascensional should instinctively disclaim the idea of opposing enables the air to exert a resisting influence as powerful on the acting surface as the force ac- he would, for the advantage of such reduction of force of lb. per foot, or 5lb. at the above speed, the thin edge of a wedge-shaped surface, because tuating that surface. This resisting influence is we readily perceive it would cleave or split the infinitely variable. It is therefore important in weight, instead of increasing his speed, decrease it air and easily pass through it. If we oppose the the highest degree to the aerial engineer to deter-to about one-half, unless he could augment his base or thick eid of the wedge the result would mine which property of air he should study to adequate density, or force without destructive effect of resistance would be still greater, even power. A primary principle in this science is widely differ, and if that end was concave the develope. When the air is in motion from natural weight, and weight without destructive surface. causes, producing what we term wind, the force. from the same uniform velocity. In this example exerted by it on stationary surfaces is propor-queries. Which is the most effective angle and anemometer or thick edge, and the bird's wing or The foregoing remarks suggest the following we have illustrated the screw or thin edge, the tional to the weight and velocity of the stream. form of surface for developing resistance? Which concave end, and the source of all our discrepanThis varies, as shown by anemometers, from an is the most economical in the consumption of ces about atmospheric resistance is here, I think, imperceptible pressure in a zephyr breeze to about 40lb. force on the square foot in a hurricane. In power? And which, therefore, will involve the conspicuous. My experiments with concave surcases of this kind the stationary surface is not the least weight and loss in its application? face propellers set at about 5deg. below the horizonactive cause of the resisting influence which it Assuming that no one will ever successfully tal line give a resistance or ascensional power of developes and encounters. Therefore the resist employ aeroplanes or screw propellers in practical about 12oz. to the square foot at a velocity not ance experienced by such surfaces is the least at- aerial engineering, we may proceed to ascertain exceeding two miles an hour. By setting the tainable from the weight and velocity of air. If the resistance developed in the employment of the wing surface at about 30deg. above the horizontal, and making the stroke in same direction as in the surface be projected into air by an indepen-concave and convex surface at low velocities. dent source of motion, the resistance experienced When we discover principles and fully appreciate previous example, the resistance was impercep by that surface would, at corresponding veloci- their importance, we become furnished with a tible, the wing surface having at that angle the ties, exceed that exerted on a stationary surface, gauge to work by, and our first endeavours will pitch of a screw propeller. This action appeared because the advancing or active surface would obviously be directed to develope their practical to me to explain the cause of birds darting sudform the apex of the column of air in its front, application. What, then, is the principle of re-denly down on their prey. By upturning the and the base would be formed by all the adjacent action in air which affords greater resistance than wing surface above the horizontal position of air set in motion thereby; whereas the stationary its simple weight? It is the preponderance of the body, as we may turn our haud and make the surface would form the base of the column of air répellative force inherent in all gaseous matter, as stroke in the perpendicular direction, gives the resisted, and its apex formed in the air advancing, previously notised. in virtue of this property the wing surface an inclination approaching the pitch the particles of which, being in motion, would air exerts, unter all circumst nees, a pressure further experiments to ascertain the resistance at of a screw, and thus cleaves the air. In making freely glide past. Accordingly military projec- equal- but ant gonistic-to gravity. Therefore, various angles, as contemplated by this society, tiles experience the greater resistance. The re-as the attractize in inence of the earth exerts a sultant effects developed in these two illustrations force on air-ner the level o the sea-equal to simply differ from the original cause of motion, 14 lb., so also does the repellent force exert an reversing the base of resistance, and not from the equal pressure, at the same point, in an opposite development of different properties of air. The and upward direction. If, then, we endeavour to point of impact of resistance is, however, in each displace either of these forces in any direction, we case at right angles to surface. In the screw pro- must evidently exert an equal force. Our chief peller we have the obtuse angle of impact in- and sole object, however, is to displace the body clined more or less to the surface, according to acting on the air, and not the air that is acted the sharpness of pitch, and the effect developed is upon. To ensure this we must find the relative a cleaving action, therefore producing less resist-weights or pressures of the bodies in question. ance, at corresponding velocities, to its passage The weight of all bodies being the measure or It remains now to find the value of the requisite through air. quantity of the effective influence of the same Military projectiles, though having convex sur-force-the earth's attraction or gravity—they are, velocity. Velocity, or time, being a primary attribute-i.e., attributable to space consumed faces, experience greater resistance than can be therefore, relative and comparable; but in the accounted for when calculated by the "law of the proportions in which the attractive or the repella- consequent on action-must, if squared, give as squares," and if they exposed concave surfaces to tive forces predominate in the matter of bodies so erroneous results in computing resistance in air, forward motion, the impact being right-angled, is the ratio of their surfaces or volumes. The air as squaring the weight to compute its power the resistance would be still greater, because of possesses but little weight in proportton to surwould do; because it cannot take cognisance of the full development of the repellent property of face or volume, and, therefore, permits dense increased density, which pressure causes air to air (due to increased density through compression) bodies-bodies possessing greater weight to suracquire as indefinitely as the continuance of the forming a cone-shaped column, the base of which face-to be projected or propelled through it with pressure or force exerted, and thereby proportionwould be in the direction of motion and its apex considerable velocity. If we compare the weight ately developes its repellent property. In virtue of the centre of concavity. By the direct action of a of a bird to the weight of the volume of air it dis- this, a reciprocating surface in arresting and resurface thus formed the point of impact is not places, we find the bird's weight to be about 600 versing the motion of advancing air in every only right-angled but also caused to converge to times greater; and, therefore, in its most compact be derived from non-repellent matter of equal stroke, encounters greater resistance than could the centre of concavity with its whole effective form could not rest or float on air. By extending force, as on a parachute, whereas with military its wing surface the bird reverses this condition density or weight, for air without this repellent projectiles the force diverges from the apex of and the air becomes a thousand times heavier on the (Concluded on page 82.) these examples indicate the necessity of defining the nature of the resistance to be developed. The resistance to forward motion of body we rethin or pointed edge. The resistance to up and quire to be reduced to a minimum ; adopt, then, the down strokes we require to be the greatest attainable; adopt, then, the concave and convex surface If a medium resistance be required use the screw or feathering surface. By setting the concave surface at an obtuse angle the screw or feathering action would be obtained. |