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may be employed, wholly or partly composed of clay tipped in front of the line of foundations, a space for which has previously been dredged to the required depth when necessary, or, in the event of clay not being within reach, an embankment may be constructed composed of the local soil, faced with clay and coated with stones in order to insure its stability. A water-tight dam is thus formed, and the excavations for the foundations may be further protected by the insertion of piles, either driven or screwed into the inner slope of the dam and also into the opposite side of the cutting. The piles have vertical grooves, into which a timber boarding may be slipped, thus forming a thoroughly dry box-dam in which foundations may be built in situ; or if no such box-dam be formed, the foundations may be sunk by means of excavators.

For the construction of bridge-piers in open water, the site may be dredged to the required depth and clay deposited, so as to form an embankment rising above water-level, down through which an excavation is made and the foundations built, or through which they may be sunk; they may also be floated into position.

To construct subways beneath water, the river-bed is dredged, and clay mixed with ground chalk and cement deposited so as to form a water-tight roof to the operations, and the subway may be formed by tunnelling through the body of the clay, ground chalk, and cement, if deposited in sufficient quantity.

The foundations may be formed of masses of stone masonry, brickwork, or concrete, whose horizontal section consists of two members at right angles to one another, these members being hollow, to permit of excavation being carried on in their interior while being sunk. Tongues or grooves of a semicircular or other shape are formed on the ends of one of the members, the other constituting a counterfort.

For the purpose of facilitating the sinking of foundations, the toe or bottom should be surrounded with a shoe or curb.

The author then described at length the drawings which were exhibited.

In conclusion he stated, it is of the utmost importance that every facility should be given to the free action of the ebb and flow of a river, because an obstruction weakens its action, thereby withdrawing a certain amount of force from its power. The advantage of these walls is that they offer comparatively little resistance to the water.

Walls of this description might be faced with hard rubble-stone of from 3, 4, 5, 6, 8, and 10 cwt. each, the remainder of brickwork or concrete. Roman cement or hydraulic lime ground with mine-dust or puzzolano might be used with advantage in the work if of rubble built in situ.

When the deposition is of great depth, as in the Clyde, varying from 60 to 90 feet in some places, the breadth of base cannot be overestimated, more particularly where subject to great weights. From this construction a base of 32 feet or more would be obtained, thereby giving great stability, also affording accommodation for water-, gas-, and sewage-pipes.

The alveus or channel of a river is subject to move upwards as well as sidewise, from causes not always in the immediate vicinity but at a distance.

On Reuleaux's Treatment of Mechanisms. By Prof. A. B. W. KENNEDY.

Importance of Hydro-Geological Surveys from a Sanitary point of view. By BALDWIN LATHAM, C.E.

The author in his paper pointed out that all subterranean stores of water were due to the rainfall percolating into the earth, but that there were matters which affected the quantity of water percolating, such as the nature of the outcrop of the strata receiving the rainfall, the volume of the strata, the lithological character, and the free communication between different parts. The water held in store in the earth did not, as a rule, maintain a horizontal level, but the surface possessed a considerable fall in directions corresponding to the points of the discharge of the springs. The inclined surface of the water pointed to its movement in the direc

tion of its outfall or natural vent. The water-level, therefore, of subterranean strata meant a line drawn from the highest point at which it accumulated to the lowest point of vent. The inclined surface of the water was the measure of the element of friction and molecular attraction which interfered with the free discharge of the water, so that it was retained in subterranean reservoirs and but slowly discharged from them. The subterranean currents obeyed the same laws, with reference to their flow, as streams which move on the surface of the earth. A number of examples were given as to the rates of fall of subterranean water, and also as to the elevation to which water did rise in particular years in the earth. It was shown that the elevation of the subterranean water between the town of Watford and the highest spring which issued from the chalk hills was 300 feet in a distance of fourteen miles, and between the Colne and the River Thames at London Bridge, a distance of fourteen miles, the water fell at the rate of 13 feet per mile. Near the Middle Chalk the rate of fall varied from 13 feet 6 inches to 19 feet 6 inches per mile, and in the Tertiary beds at Garrett the fall was 5 feet per mile, and in the same formation at Waltham Abbey 4 feet per mile. The well of Grenille, in the Lower Greensand, indicated a fall of 2 feet per mile. A table was given showing the rate of fall of subterranean water in the neighbourhood of Croydon, which was shown to vary from 8 feet per mile to 94 feet per mile; and the subterranean water, as ascertained by wells sunk in the boulder-clay at East Dereham, Norfolk, showed that the water-level varied from 2 feet in a mile in the flat tableland to 100 feet in a mile in the valleys. The author pointed out the importance of pure water with regard to health, and gave several examples showing the deleterious effects of the drainage from cesspools and cemeteries upon watersupply and the health of the persons using it; he also pointed out the importance of ascertaining the direction in which subterranean water was moving, in reference to the construction of wells and cesspools, and that a small amount of consideration with regard to the relative positions of the well and cesspool in a countryhouse may make all the difference between rendering it healthy or unhealthy. With regard to epidemics of enteric fever, whether directly ascribed to water or milk, the author observed that in every case recorded the water had invariably been procured from wells; and while it was singular that so much attention was paid to the pollution of rivers flowing over the surface of the ground, which had never been traced to be the cause of disease, no one had thought of the great evils which had resulted, and would result, from the pollution of underground sources of water-supply. The object of the author was to direct attention to this important subject, and to point out that where the use of cesspools was unavoidable, there were ways in which they might be introduced without the possibility of polluting the water-supply when it can only be procured from a local well.

On the Direct Motion of Steam-Vessels. By R. MANSEL.

On the Strength and Fracture of Cast Iron. By W. J. MILLAR. The object of the present communication is to describe certain phenomena observed by the writer when engaged in testing cast-iron bars.

The bars were about 40 inches long, 2 inches deep, and 1 inch broad. The distance between supports (or span) when placed in testing-machine was 36 inches. The load was applied gradually and at centre of span.

In general the bars broke with straight fractures; the direction of fracture being in line of application of load. In some cases, however, curved forms of fracture were observed.

During the course of testing it was observed that the curved fractures divided the span more or less unequally, whilst the straight fractures, with few exceptions, divided the span into equal portions.

After a carefully conducted series of experiments, the writer finds that the form of fracture conclusively points out the position of fracture, viz. that bars showing straight fractures have broken at or close to centre of span, whilst bars

showing curved fractures have broken at points more or less removed from centre of span, and that in general the curve of fracture increases with distance of fracture from centre.

In all cases the fractured parts were found to fit exactly together, no piece of the metal being thrown out on fracture taking place; and where the fractures were curved the line of fracture pointed towards point of application of load, the results of several experiments showing that fracture commences at the convex side of the bar and passes upwards, gradually curving towards centre of span.

The curved fractures occur also in bars of 1 square inch section, their forms not being, however, so well marked as in the bars already referred to.

With a view to obtain the relative strength of bars showing straight and curved fractures, a note was kept of the breaking loads, deflection, forms, and positions of fracture, the result of which is given in Table I.

(The results given in the following Tables are all from bars of 2 inches deep, 1 inch broad, and 36 inches span.)

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The above results show a slight excess of strength in bars breaking at centre of span and with straight fractures.

In general the deflections were found to increase with increase of load; but in some cases, the bars being exceptionally strong and remaining unbroken, a decrease of deflection accompanied an increase of load.

The results obtained from 14 such bars are shown in Table II.

TABLE II.

Average results obtained from 14 unbroken bars with increasing Loads.

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Table III. contains the results of some experiments made to determine the amount of "set" which took place in bars when subjected to several applications of the same load.

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From these experiments it appears that the "set" decreases with successive applications of the same load.

This decrease of set also appears to obtain even when the load applied is an increasing one.

The results obtained from 10 bars are given in Table IV.

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On a Spherical Pendulous Safety-Valve. By JAMES NASMYTH, F.R.S.

On the Investigation of the Steering Qualities of Ships. By Prof. Osborne REYNOLDS.

[Printed in extenso among the Reports, p. 70.]

On a New Form of Lamp. By R. LAVENDER.

The construction of the lamp is a glass lantern 18 inches square, with a funnel or chimney 24 inches high, into which is introduced a jet of steam about inch across when the pressure of steam is about 201b. to 30 lb. per square inch; if the pressure is less the jet must be larger, if higher smaller, the object of the jet being to create a partial vacuum in the lantern-the consequence being that the surrounding air is forced through the burner of the lamp and causes a very complete combustion of the oil.

A very brilliant light is produced, which is increased partly owing to the products of combustion being continuously removed and a volume of fresh air being introduced.

The lamp or burner is constructed for a circular wick, and upon the principle of admitting the air to play upon the outside of the wick, and also by a disk another column is thrown upon the inside of the wick; another current of air is also carried through the centre of the flame. The metal cap is constructed so as to bring the flame into a centre, through the orifice of which it is drawn by the jet of steam in the chimney. The oil supply is contained in a shallow vessel, which is heated by a jet of steam before being burned, as many of the oils that may be used would become thick in cold weather.

The results obtained from a 4-inch wick have been equal to a light of upwards of six hundred sperm candles, the cost of which, with oil at 9d. per gallon, is under 1d. per hour. The oil was supplied by Messrs. Young's Paraffin Light Company, and is a product from shale and is a part of the oil that hitherto has been of little use.

The cost of burning an open fire, such as is used at many pit-heads, is from ten to twelve hundredweight of coal per night; it is a most uncertain and dangerous light.

Whilst the author's lamp was designed for collieries, loading-banks, sheds, sidings, ships, &c., he thinks that it will be of great service to the public.

On Boiler Incrustation and Corrosion. By F. J. ROWAN.

The importance of the subject is alluded to, especially to marine engineers, who have most keenly felt its difficulties, while the range of interests involved by it is as wide as the use of steam.

The present state of general information about it being unsatisfactory, we have 1876.

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to seek in a combination of chemistry and mechanical science for the needed elucidation of its problems.

The course of investigation has been marked by the suggestion of various empirical remedies, which are pointed out, but which have failed to reach any good result, the actions to be counteracted not being understood.

Incrustation and corrosion are not one action, but dissimilar ones, although they are often found united in boilers, and therefore both must be noticed.

Incrustation is first considered, Dr. J. G. Rogers, of Madison, U. S., being quoted (from 'Chem. News,' vol. xxvi.) for the non-conductibility of crusts and the proportionate increase of temperature which their presence in boilers renders necessary. Boilers subject to incrustation are divided into two classes :

1. Land boilers using natural fresh waters; and

2. Marine boilers using sea-water.

1. The average quality of natural fresh waters is illustrated by analysis of RiverClyde water, as formerly supplied to Glasgow; and an analysis also by Dr. Wallace of crust deposited from that water is given. The case is then quoted of the boilers at a mill in Barrowfield still using that water, but in which the formation of crust is prevented by the use of a quantity of soda-ash.

The action of soda-ash under these circumstances is described; it causes the decomposition of the sulphate of lime and rapid deposition of the neutral carbonate as powder. Where bicarbonate of lime is present, it is also precipitated as neutral carbonate in a powdery form, one equivalent of carbonic acid being liberated. Neutral carbonate being thus formed rapidly, has not power to adhere to boiler surfaces; while, if deposited slowly by heat from the bicarbonate, it is crystalline

and does adhere.

M. Bidard of Rouen, author of papers on this subject in Annales Industrielles,' has made numerous examinations of boiler-crusts, which show, according to him, that organic matter has power to agglomerate carbonate of lime and form crust by a process of "baking." His opinion is quoted from one of his letters to the

author.

Fresenius, quoted in a paper by Dr. Wallace in 'Proc. of the Phil. Soc. of Glasgow,' vol. iv., ascribes this agglomerating power to sulphate of lime. Bidard's explanation applies where carbonate and not sulphate of lime predominates, because sulphate is able to form crusts where no organic matter is present, as in some crusts from marine boilers. The use of too much soda-ash is injurious, and precautions are given, with a little further illustration of its action in boilers.

It is proposed to apply it in the feed-tanks or cisterns generally attached to boilers, allowing the lime to be deposited there to save constant blowing off.

Various other preventives of incrustation are noticed, including De Häen's method of using barium chloride and milk of lime, founded upon the investigations of J. Y. Buchanan (Roy. Soc. Proc. vol. xxii.), and some details of comparative cost in working with this process are given from Dingler's Polyt. J. ccxvii.

As the most complete preventive of incrustation, which is otherwise scientifically desirable, the author advocates the use of surface condensers in connexion with land boilers.

2. Although modern systems of marine engine practice have removed incrustations from marine boilers by the introduction of surface condensation, there is still some necessity to consider incrustation as applying to them, because of a tendency to return to the ancient régime in consequence of difficulties with corrosion. The evil effects of incrustation are felt more heavily in marine practice from its conditions of using sea-water, which contains a large amount of solids, and of limited space for carrying fuel and chemical reagents and for repair of boilers.

The inapplicability of the chemical method is pointed out, reference being made to experiments of Mr. Jas. R. Napier, F.R.S., published in Proc. Phil. Soc. Glasg. vol. iv.

Working with fresh water is the only sensible and efficacious method; but when this has been used it has brought with it the evils of corrosion.

Analyses of sea-water from the Black Sea, and of six samples of marine-boiler crusts found at various pressures, are added, with remarks on some of these by Dr. Wallace (from Proc. Phil. Soc. Glasg.), and extracts from a paper in Dingler's

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