REPORTS OF COMMITTEES. In response to the letter of Professor Redwood the Committee recommended that the fees for the Chemistry The report of this Committee was read and adopted, and Pharmacy course be increased to the following and sundry accounts ordered to be paid. BENEVOLENT FUND. The report of this Committee was read, including reconmendations of the following grants: 40 to a registered chemist and druggist in distressed circumstances. Applicant has received a former grant of like amount. £.0 to a former member, aged 55, who has had two former grants. One application had been rejected, the person seeking assisance being in receipt of parochial relief; and another applcation had been ordered to stand over. The following regulation of the Royal Agricultural Benevolent Institution had been laid before the Committee by the Secretary, who suggested that a similar regulation might with advantage be adopted :— "Should any subscriber, being duly qualified, hereafter become a candidate for the benefits of the Institution such number of votes should be placed to his or her credit at the first succeeding election, as should be represented by the whole amount of subscription he or she may have paid during the period of his or her enrolment as a subscriber." The consideration of this matter had been deferred to the next meeting of the Committee. amounts: One Course. An Entire Session £3 38. The report and recommendations of the Committee were received and adopted. THE PHILADELPHIA EXHIBITION, The PRESIDENT read a letter received from the American Pharmaceutical Association expressing a hope that many English pharmacists visiting the Philadelphia at the annual meeting of the Association in September. Exhibition would make arrangements for being present APPOINTMENT OF PROFESSORS and Curator FOR Professor Redwood was re-appointed Professor of Professor Bentley was re-appointed Professor of Botany and Materia Medica for the ensuing year. Professor Attfield was re-appointed Professor of HOUSE. The report of this Committee was read and adopted. It only referred to matters of detail with regard to the The report and recommendations were received and house arrangements. adopted. LIBRARY, MUSEUM, AND LABORATORY. The report of this Committee included the following information: Professor Redwood had reported that he had 51 students now attending his class; 15 perpetual, and 12 for the entire session. Professor Bentley had reported 74 students in his class. Professor Attfield had reported that he had had 119 entries since the commencement of the session, 56 now working. The LIBRARIAN reported that the average attendance in the Library during the day had been 27; in the evening 9. The circulation of books had been 174 in town; country, to 28 places, 47. The Committeee recommended the purchase of the following books from the general fund :- Clowes' 'Practical and Analytical Chemistry.' : A series of specimens illustrating a paper on Ergot, by Professor Dragendorff of Dorpat. A fine specimen of Bryony root, from Mr. Sturton, of Cambridge. A number of specimens of Indian drugs, from Professor Dymock, of Bombay. Specimen of the root of Garuleum bipinnatum, from the Cape of Good Hope, from Mr. Hyman. With regard to the question recently raised as to the obtaining for the library certain foreign pharmaceutical journals, Mr. Greenish had reported that he had made inquiries of a firm of booksellers in Berlin who had furnished an estimate. The Committee decided to defer the consideration of this question until next month, further inquiries to be made in the meantime. LAW AND PARLIAMENTARY. The report of this Committee contained letters from the Solicitor detailing the steps taken in various legal proceedings. The Secretary also reported steps taken in several cases of alleged infringement of the Pharmacy Act. The Committee recommended prosecution in four cases of infringement of the provisions of the Pharmacy Act, 1868. The report of the Committee was received and adopted. The following Superintendents and Deputy-Superintendents of written examinations at the various local centres, were appointed for the ensuing year : SUPERINTENDENTS OF EXAMINATIONS. Aberdeen Berwick-on-Tweed Carmarthen Colchester Edinburgh Inverness Carr, Robert. .Churchill, Walter J. .Haller, Frederick William. Evans, C. .Prosser, E. T. Hutchinson, E. ...Shaw, H. W. Durden, Henry. Edinburgh Ainslie, William. THE COUNCIL EXAMINATION PRIZES. Messrs. Carteighe and Linford were appointed to conduct the examination for the Council Examination Prizes to be held on Wednesday, the 26th instant. The SECRETARY read a letter from Mr. Mackay, saying that the Council of the North British Branch had received an application from Dr. Gillespie on behalf of the Edinburgh Medical and Chirurgical Society, for the use of the Society's Rooms once a month, paying a fee of one guinea. The Council of the North British Branch had acceded to the application subject to the approval of the London Council. A. resolution was passed sanctioning the proposed arrangement. A letter was read from a gentleman who prepares pupils for the examinations of the Society, asking that the list of successful candidates might be made known to him on the evening of the day of examination, instead of the next morning, in order to save young men from a night of suspense, and allow some of them to return to their homes a day earlier. The SECRETARY said the list used to be exhibited in the hall on the night of the examination, but the practice had given rise to much confusion and obstruction in the hall, and it became absolutely necessary to discontinue it, The candidates were now communicated with direct from the office, and that system has been found to work satisfactorily. The Secretary was directed to inform the gentleman referred to that the Council could not accede to his request, THE PRELIMINARY EXAMINATIONS. The SECRETARY submitted the following list of attendances at the different centres since the establishment of the present system : Proceedings of Scientific Societies. ROYAL INSTITUTION OF GREAT BRITAIN.* BY W. CROOKES, F.R.S. The speed with which a sensitive radiometer will revolve in the sun is almost incredible; and the electric light such as I have in this lantern cannot be far short of full sunshine. Here is the most sensitive instrument I have yet made, and I project its image on the screen, letting the full blaze of the electric light shine upon it. Nothing is seen but an undefined nebulous ring, which becomes at times almost invisible. The number of revo lutions per second cannot be counted, but they must be several hundreds, for one candle has made it spin round forty times a second. I have called the instrument the radiometer, because it will enable me to measure the intensity of radiation falling on it by counting the revolutions in a given time; the law being that the rapidity of revolution is inversely as the square of the distance between the light and the instrument. When exposed to different numbers of candles at the same distance off, the speed of revolution in a given time is in proportion to the number of candles; two candles giving twice the rapidity of one candle, and three, three times, etc. The position of the light in the horizontal plane of the instrument is of no consequence, provided the distance is not altered; thus, two candles, 1 foot off, give the same number of revolutions per second, whether they are side by side or opposite to each other. From this it follows that if the radiometer is brought into a uniformly lighted space it will continue to revolve. It is easy to get rotation in a radiometer without having the surfaces of the discs differently coloured. Here is one having the pith discs blacked on both sides. I project its image on the screen, and there is no movement. I bring a candle near it, and shade the light from one side, when rapid rotation is produced, which is at once altered in direction by moving the shade to the other side. I now move the candle a little distance off, so as to make the instrument move slower, and bring a flask of boiling water close to it. See what happens. The luminous index no longer moves steadily, but in jerks. Each disc appears to come up to the boiling water with difficulty, and to hurry past it. More and more sluggishly do they move past, until now one has failed to get by, and the luminous beam, after oscillating to and fro a few times, comes to rest. I now gradually bring the candle near. The index shows no movement. Nearer still. There is now a commencement of motion, as if the radiometer was trying to push past the resistance offered by the hot water; but it is not until I have brought the candle to within a few inches of the glass globe that rotation is recommenced. On these pith radiometers the action of dark heat is to repel the black and white surfaces almost equally, and this repulsion is so energetic as to overcome the rotation caused by the candle, and to stop the instrument. With a radiometer' constructed of a good conductor of heat, such as metal, the action of dark heat is different. Here is one of silvered copper, polished on one side and lampblacked on the other. I have set it moving with a candle slightly the normal way. Here is a glass shade heated so that it feels decidedly warm to the hand. I cover the radiometer with it, and the rotation first stops, and then recommences the reverse way. On removing the hot shade the reverse movement ceases, and normal rotation recommences. diometer the arms at once revolve the normal way, as if If, however, I place a hot glass shade over a pith raI had exposed the instrument to light. The diametrically opposite behaviour of a pith and a metal instrument when exposed to dark heat radiated from a hot glass shade is very striking. The explanation of the action is not easy, but it depends on the fact that the metal is one of the best conductors of heat, whilst pith is one of the worst. : One more experiment with this metallic radiometer. I heat it strongly with a spirit lamp, and the arms spin round rapidly. Now the whole bulb is hot, and I remove the lamp see what happens. The rotation quickly diminishes. Now it is at rest; and now it is spinning round just as fast the reverse way. I can procure this reverse movement only with difficulty with a pith instrument. The action is due to the metal being a good conductor of heat. As it absorbs heat it moves one way; as it radiates heat it moves the opposite way. I have arranged here a radiometer so that it can be made to move by a very faint light, and at the same time its rotation is easily followed by all present. In this At first I made these instruments of the very lightest bulb is a large six-armed radiometer carrying a mirror in material possible, some of them not weighing more than its centre. The mirror is almost horizontal, but not half a grain; and where extreme sensitiveness is required quite so, and therefore when I throw a beam of electric lightness is essential. But the force that carries them light vertically downwards on to the central mirror, the round is quite strong enough to move a much greater light is reflected off at a slight angle, and as the instru-weight. Thus the metallic instrument I have just experiment rotates its movement is shown by the spot of light mented with weighs over 13 grains, and here is one still travelling round the ceiling in a circle. Here again the heavier, made of four pieces of looking-glass blacked on fog helps us, for it gives us an imponderable beam of the silvered side, which are quickly sent round by the light moving round the room like a solid body, and saving impact of this imponderable agent, and flash the rays of you the trouble of looking up to the ceiling. I now set light all round the room when the electric lamp is turned the radiometer moving round by the light of a candle, and I want to show you that coloured light does not very much interfere with the movement. I place a yellow glass in front, and the movement is scarcely diminished at all. Very deep coloured glass, you see, diminishes it a little more. Blue and green glass make it go a little slower, but still do not diminish the speed one half. I now place a screen of water in front: the instrument moves with diminished velocity, rotating with about onefourth its original speed. Taking the action produced by a candle flame as 100 89 71 * Lecture delivered on Friday, February 11, 1876. on the instrument. Before dismissing this instrument, let me show one more experiment. metal radiometer side by side, and, screening the light I place the looking-glass and the from them, they come almost to rest. Their temperature is the same as that of the room. What will happen if I suddenly chill them? each of the bulbs. I pour a few drops of ether on Both instruments begin to revolve. But notice the difference. Whilst the movement in the case of the metal radiometer is direct, that of the lookingglass instrument is reverse. And yet to a candle they both rotate the same way, the black being repelled. Now, having found that this force would carry round a comparatively heavy weight, another useful application suggested itself. If I can carry round heavy mirrors or plates of copper, I can carry round a magnet. Here then is an instrument carrying a magnet and outside is a smaller magnet, delicately balanced in a vertical position, having the south pole at the top and the north pole at the botom. As the inside magnet comes round, the outside magiet being delicately suspended on its centre, bows backyards and forwards, and, making contact at the botton, carries an electric current from a battery to a Morse instrument. A ribbon of paper is drawn through the "Morse" by clockwork, and at each contact—at each revolution of the radiometer-a record is printed on the strip of paper by dots; close together if the radiometer revolves quickly, farther apart if it goes slower. Here the inner magnet is too strong to allow the radiometer to start with a faint light without some initial impetus. Imagine the instrument to be on the top of a mountain away from everybody, and I wish to start it in the morning. Outside the bulb are a few coils of insulated copper wire, and by depressing the key for an instant I pass an electric current from the battery through them. The interior magnet is immediately deflected from its north-south position, and the impetus thus gained enables the light to keep up the rotation. In a proper meteorological instrument I should have an astatic combination inside the bulb, so that a very faint light would be sufficient to start it, but in this case I am obliged to set it going by an electric current. I have placed a candle near the magnetic radiometer. I now touch the key; the instrument immediately responds; the paper unwinds from the Morse instrument, and on it you will see dots in regular order. I put the candle 8 inches off, and the dots come wide apart. I place it 5 inches off, and two dots come where one did before. I bring the candle 4 inches from the instrument, and the dots become four times as numerous, thus recording automatically the intensity of the light falling on the instrument, and proving that in this case also the radiometer obeys the law of inverse squares. This instrument, the principle of which I have illustrated to-night, is not a mere toy or scientific curiosity, but is capable of giving much useful information in climatology. You are well aware that the temperature, the rainfall, the atmospheric pressure, the direction and force of the wind, are now carefully studied in most countries, in order to elucidate their sanitary condition, their animal and vegetable productions, and their agricultural capabilities. But one most important element, the amount of light received at any given place, has been hitherto but very crudely and approximately estimated, or rather guessed at. Yet it cannot be denied that sunlight has its effect upon life and health, vegetable, animal, and human, and that its relative amount at any place is hence a point of no small moment. The difficulty is now overcome by such an instrument as this. The radiometer may be permanently placed on some tall building, or high mountain, and, by connecting it by telegraphic wires to a central observatory, an exact account can be kept of the proportion of sunlight received in different latitudes, and at various heights above the sea level Furthermore, our records of the comparative temperature of different places have been hitherto deficient. The temperature of a country depends partly on the amount of rays which it receives direct from the sun, and partly on the atmospheric and oceanic currents, warm or cold, which sweep over or near it. The thermometer does not discriminate between these influences; but the radiometer will enable us now to distinguish how much of the annual temperature of a place is due to the direct influence of the sun alone, and how much to the other factors above referred to. I now come to the last question which I stated at the beginning of this discourse, "What is the amount of force exerted by radiation?" Well, I can calculate out the force in a certain way, from data supplied by this torsion apparatus. Knowing the weight of the beam, the power of the torsion fibre of glass, its time of oscillation, and the size of the surface acted on, it is not difficult to calculate the amount of force required to deflect the beam through a given angle; but I want to get a more direct measure of the force. I throw a ray of light upon one of these | instruments, and it gives a push; surely it is possible to measure the amount of this push in parts of a grain. This I have succeeded in doing in the instrument behind me; but before showing the experiment I want to illustrate the principle upon which it depends. Here is a very fine glass fibre suspended from a horizontal bar, and I wish to show you the strength of it. The fibre is only a few thousandths of an inch thick; it is about 3 feet long, and at the lower end is hanging a scale-pan, weighing 100 grains. So I start with a pull of 100 grains on it. I now add little lead weights, 50 grains each, till it breaks. It bears a pull of 750 grains, but gives way when additional weight is added. You see then the great strength of a fibre of glass, so fine as to be invisible to all who are not close to it, to resist a tensile strain. Now I will illustrate another equally important property of a glass thread, viz., its power to resist torsion. Here is a still finer glass thread, stretched horizontally between two supports: and in order to show its position I have put little jockeys of paper on it. One end is cemented firmly to a wooden block, and the other end is attached to a little instrument called a counter-a little machine for registering the number of revolutions. I now turn this handle till the fibre breaks, and the counter will tell me how many twists I have given this fibre of glass. You see it breaks at twenty revolutions. This is rath ra thicker fibre than usual. I have had them bear more than 200 turns without breaking, and some that I have worked with are so fine that if I hold one of them by the end it curls itself up and floats about the room like a piece of spider's thread. Having now illustrated these properties of glass fibres I will try to show a very delicate experiment. I want to ascertain the amount of pressure which radiation exerts on a blackened surface. I will put a ray of light on the pan of a balance, and give you its weight in grains; for I think in this Institution and before this audience I may be allowed a scientific use of the imagination, and may speak of weighing that which is not affected by gravitation. The principle of the instrument is that of W. Ritchie's torsion balance, described by him in the Philosophical Transactions,' for 1830. The construction is somewhat complicated. A light beam, AB, having 2 square inches of pith, C, at one end, is balanced on a very fine fibre of glass, DD, stretched horizontally in a tube; one end of the fibre being connected with a torsion handle, E, passing through the tube, and indicating angular movements on a graduated circle. The beam is cemented to the torsion fibre, and the whole is enclosed in glass and connected with the mercury pump by a spiral tube, F, and exhausted as perfectly as possible. G is a spiral spring, to keep the fibre in a uniform state of tension. H is a piece of cocoon silk. I is a glass stopper, which is ground into the tube as perfectly as possible, and then highly polished and lubricated with melted indiarubber, which is the only substance I know that allows perfect lubrication and will still hold a vacuum. The pith, C, represents the scalepan of the balance. The cross-beam, A B, which carries it, is cemented firmly to the thin glass fibre, D, and in the centre is a piece of mirror, K. Now the cross-beam A B, and the fibre, D, being rigidly connected together, any twist which I give to the torsion handle, E, will throw the beam out of adjustment. If, on the other hand, I place a weight on the piece of pith C, that end of the beam will fall down, and I shall have to turn the handle, E, round and round a certain number of times, until I have put sufficient torsion on the fibre, D, to lift up the beam. Now, according to the law of torsion, the force with which a perfectly elastic body like glass tends to untwist itself is directly proportional to the number of degrees through which it has been twisted; therefore, knowing how many degrees of torsion I must put on the fibre to lift up the th of a grain weight, I can tell how many degrees of torsion are required to lift up any other weight; and con |