June 6, 1878. The Annual Meeting for the election of Fellows was held this day. Sir JOSEPH HOOKER, K.C.S.I., President, in the Chair. The Statutes relating to the election of Fellows having been read, Major-General H. Clerk and Dr. G. Johnson were, with the consent of the Society, nominated Scrutators to assist the Secretaries in examining the lists. The votes of the Fellows present having been collected, the following candidates were declared duly elected into the Society. John Gilbert Baker, F.L.S. John Hughlings Jackson, M.D. Edward Albert Schäfer, M.R.C.S. Charles Sissmore Tomes, M.A. Thanks were given to the Scrutators. June 20, 1878. Sir JOSEPH HOOKER, K.C.S.I., President, in the Chair. In pursuance of the Statutes, notice of the ensuing Anniversary Meeting was given from the Chair. The Presents received were laid on the table and thanks ordered for them. The Right Hon. William Henry Smith, Mr. John Gilbert Baker, Mr. Francis Maitland Balfour, Prof. James Henry Cotterill, Sir Walter Elliot, Rev. Canon W. Greenwell, Mr. Thomas Hawksley, Dr. John Hopkinson, Mr. Samuel Roberts, Mr. George James Symons, and Mr. Charles Sissmore Tomes, were admitted into the Society. The following Papers were read : I. "Notes on Physical Geology. No. V. Mr. George H. Darwin's Comments on Note No. III." By the Rev. SAMUEL HAUGHTON, M.D. Dubl., D.C.L. Oxon, F.R.S., Professor of Geology in the University of Dublin. Received May 20, 1878. In the "Proceedings of the Royal Society," 14th March, 1878, p. 179, Mr. George H. Darwin has published a criticism on my proposed method of finding a limit to the duration of certain geological periods, published in the "Proceedings of the Royal Society," 20th December, 1877, p. 534. My paper, of 20th December, consisted of two parts:-1st. A discussion of the rate at which a "wabble" of the earth's axis of rotation, caused by a want of coincidence between the axis of figure and the axis of rotation, would be destroyed by the friction of the ocean" against its bed. 2nd. Speculative inferences from the solution of this problem, as to the duration of geological periods, depending on hypothetical geological assumptions as to the method in which Europasia was manufactured. These assumptions were three in number, and none of them very probable, viz. : (a.) An instantaneous formation of the continent; (b.) Its formation by means of 69 equal convulsions, with an interval of time between each, sufficient to reduce the radius of the wabble from one mile to five feet; (c.) Its formation, by a number of small shocks, each displacing the axis of figure by such an amount that tidal friction would be able to render the axes of figure and rotation again coincident in the period of a single wabble. In discussing the two latter hypotheses, I naturally timed my shocks so as to produce the maximum wabble. For this assumption I have, of course, no authority; and I readily admit that any conclusions drawn from the earth's wabble can have no more value than the probability of the hypothesis we may make as to the method of formation of Europasia. In general, let AOB, fig. 1, be a portion of the path described by the axis of the figure, let AO be the displacement produced by any single shock, and let APBQ be the circle described by the axis of rotation in the first wabble after the occurrence of the shock. If the next shock which moves the axis of figure from 0 to B occurs when the axis of rotation is at A, the wabble will be doubled, and have the radius AB; but if the second shock be so timed as to occur when the axis of rotation is passing through B, the wabble will immediately cease, for the axes of rotation and of figure will coincide.* If 304 75 days, the wabble will be doubled if the next shock occurs at an interval denoted by nr, and will be destroyed if the interval is (n + 1)T. If the shocks occur at irregular intervals, at the moment of shock the axis of rotation may be anywhere on the circle APBQ, and the mean effect will be found when the axis is at P or Q, which would be a more probable assumption than that made by me, when I placed the axis always at A. Let us now calculate the mean effect when shocks occurring at unknown intervals take place when the axis of rotation is at P or Q. Let r denote the radius AO, then we have Radius of 1st wabble = r. If r5 feet (the least observable wabble), n, the number of equal shocks required to displace the axis of figure through 69 miles, will be and n= 69 × 5280 =72,864, √n=270. This number should be substituted for A' in equation 12 (Note iii, p. 543), when we obtain, for the number of years required by tidal friction to destroy the final wabble, 320,380 years. This, as might be expected, is half the time required to destroy the final wabble, when all the shocks were additive at a maximum and occurred when the axis of rotation was passing through A. Mr. Darwin has discussed at length the case of the axis of figure moving uniformly, and finds that the axis of rotation will move on a cycloid. I here give an easy geometrical proof of this theorem : Let AOB be a portion of the path uniformly described by the axis * If AB be 69 miles, Europasia might have been manufactured in 152 days, by two equal shocks. of figure; and let z be the position of the axis of figure at any moment, and y the corresponding position of the axis of rotation, then by the conditions of the problem, fig. 2, Ax varies as the time, The angle, Axy=yzz varies as the time. But the angle yzz is proportional to the arc ay: therefore Ax varies as arc yx, but they are supposed to start together from zero, at the point A. Therefore Ax = arc xy, and the locus of y is the common cycloid, whose generating circle is xyz with diameter equal to the axis of the cycloid PO. If the axis of figure therefore travels uniformly, the axis of rotation will describe a cycloid, and the two axes will coincide every 152 days, at the cusps, and the maximum radius of wabble will be OP, the diameter of the generating circle. Mr. Darwin, finally, discusses the following problem :* "I will now suppose that the geological changes begin suddenly from rest and proceed at such a rate that the variations in the position of the principal axis are imperceptible to astronomical observation. I will suppose, therefore, that the extremity of the instantaneous axis is never more than 5 feet distant from the extremity of the principal axis." Mr. Darwin deduces from this that a displacement in the axis of figure, amounting to 69 miles, might be produced in 19,200 years, without ever producing an observable wabble. My calculation of this problem is as follows: Since OP is 5 feet, the base of the cycloid, AB will be 57, and as this length is described by the axis of figure in half a wabble, we have, if x be the number of years required to describe 69 miles, This result is half that obtained by Mr. Darwin. My object in publishing the latter part of my paper, was to show that if geologists shall ever be in a position to give us exact information as to the mode of formation of a continent, under certain circumstances, conclusions of value as to geological time might be deduced from observations made on the wabble of the axis of rotation; but it is clear that, in the present state of our knowledge, such conclusions must be regarded as hypothetical. Ante, p. 182. II. "On the Acceleration of Oxidation by the Least Refrangible End of the Spectrum." Note II. By Captain ABNEY, R.E., F.R.S. Received June 8, 1878. In my first note on this subject it was stated that further experiments would be undertaken, in which sensitive films would be exposed to the action of the spectrum in atmospheres free from oxygen. These have been carried out by means of apparatus specially designed for the purpose, hydrogen and nitrogen being the atmospheres employed, and in some cases hydrogen vacua. In every case the experiments were confirmatory of what was previously surmised, the image showing no signs of oxidation, and there is evidence to show that the limit of sensibility of the compounds used is lowered towards the least refrangible end of the spectrum. Exposure of films in solutions which readily combine with oxygen, and at the same time with the halogens, have given most remarkable results. For instance, silver bromide which by its colour should have proved sensitive to the red end, yet when exposed in the usual manner was insensitive below B in the spectrum, proved sensitive when exposed in sodium sulphite (Na2SO3), and arrived at M the lowest limit (about W.L. 12,000) which I have as yet photographed. In the same solution, to quote another experiment, silver iodide proved sensitive to a point between a and A. The experiments were carried out in duplicate. In one the plate was immersed in the solution, and in another the salt was dissolved when possible in glycerine and applied to the film. Both methods answered equally well, but for some purposes the latter is more convenient. My experiments also prove, that what is technically known as solarization is due to the oxidation of the image, accelerated by light generally, be it the more or less refrangible end of the spectrum. This oxidation causes the formation of a compound which is undevelopable, as already has been pointed out. It has thus been found impossible to produce solarization in solutions which have oxygen absorbents. We may therefore conclude that the whole spectrum exercises a reducing action on the sensitive salt, and that this reduced compound is again capable of being oxidized by it. The relative power of the two actions seems to vary according to the part of the spectrum. This subject is still under consideration. In my first note I also mentioned that photography in natural colours probably depended on the same action. My surmise is confirmed to a great extent. If silver sub-chloride or silver sub-bromide be produced chemically, we have a dark compound formed which, if exposed to the action of the spectrum whilst in an oxidizing solution (such as hydrogen peroxide), rapidly takes the colour of the rays acting upon it, |