438 



NATURE 



\Sept. 1 6, 1875 



been appointed to investigate the methods of making gold assays 

 and stating the results. It stated that the standard gold plate 

 had now been finished, and that portions of it had been forwarded 

 to different mints for the purpose of being assayed. The reports 

 read were very satisfactory, as was shown by the fact of M. Stas, 

 of Brussels obtaining 999 "95 parts of pure gold out of 1,000 as 

 the result of an analysis. The same plate had also been exa- 

 min 3d by Mr. Lockyer by means of the spectroscope, and the 

 lines having been compared with the solar lines, it had been 

 shown that silver, copper, and iron were absent, and that there- 

 fore the purification of the metal had been very great. 



Mr" A. H. Allen read the Report of the committee appointed 

 for the urpose of examining and reporting upon the methods 

 employed pin the estimation of potash and phosphoric acid in 

 commercvj t products, and on the mode of stating the results, in 

 which he stated the object of this committee was to examine all 

 the known methods of analysis of manures and potassium salts. 

 They had hoped to be able now to present to the Section some 

 practical and easy process as a neutral standard of reference by 

 which the present discrepancies might be avoided. The plan 

 adopted by the committee was to draw up a printed list of 

 queries which were sent round to all the members of the 

 Chemical Society, with the request that they would send back 

 answers ; this plan had been found to work well with very few 

 exceptions, who declined to give up the processes which they 

 alone employed. The report ended by the committee desiring 

 to be re-appointed, and expressing a confident expectation that 

 by the end of another year some really good results would be 

 obtained. — The President remarked, at the conclusion, that the 

 estimation of potash seemed to present much less difficulty than 

 that of phosphoric acid. 



Second Report of a Committee, '-consisting of Prof. A. S. 

 Herschel and G. A. Lebour, on Experiments to determine 

 the Thermal Conductivities of certain Rocks, showing especially 

 the Geological Aspects of the Investigation.— 1)^^ experiments 

 during the past year were directed chiefly to a re-examina- 

 tion, with improved apparatus (fully described in the report), of 

 the rocks observed last. year. With the exception of Kenton 

 sandstone, which was m^* placed in the last table, all the rocks 

 have, under the new mode of treatment, kept the same relative 

 positions, and the absolute conductivities given in the present 

 report are believed to leave little or nothing to be desired on the 

 score of accuracy. Quartz has been added to the list, and proves 

 to have less resistance to the passage of heat than any of the 

 other substances examined. Slate has been tried both in the line 

 of cleavage and across it, showing fcj- resistance in the latter posi- 

 tion than in the former. Some rocks have been experimented 

 on wet as well as dry, the addition of the water giving an 

 increased conductivity of a tolerably constant value. It is 

 intended to continue the experiments in the direction fore- 

 shadowed by these results. A full table of absolute conduc- 

 tivities and resistances, with the results of both series of experi- 

 ments compared, forms part of the report. Coal still maintains 

 its position with the greatest resistance yet found. 



SECTIONAL PROCEEDINGS 

 SECTION A— Mathematics and Physics 



Captain Abney read a paper On the Increase of Actinism dt.' 

 to difference of Motive Power in the Electric Light, in which he 

 stated that having been called upon by the War Office to under- 

 take the photometric measurements of certain magneto-electric 

 lights, he had determined to carry out actinic measurements of 

 their value at the same time, believing that the eye observations 

 would be closely checked by such an independent method. In the 

 first comparison of the results obtained by both kinds of mea- 

 surement, a considerable discrepancy was found to occur in the 

 values given to the different lights. The photographic records 

 could not err except through gross carelessness in the chemical 

 preparations, and against this every precaution had been taken. 

 At first it seemed likely that the eye observations were in fault, 

 but a more critical examination convinced Captain Abney that 

 both were correct ; and that though the curves obtained for the 

 values of the lights did not coincide, yet that they did act as a 

 check, the one on the other. In all there were six different 

 machines to examme, each of which was driven by a ten-horse 

 power engine. Several were driven at varying speeds that the 

 difference in the light caused by the variation might be tested. 



The eye observations were made by a little instrument called 

 by Captain Abney the Diaphanometer, and described in the 

 Monthly Notices of the Astronomical Society for last June. The 



method adopted for registering the actinic power of the light was 

 by exposing uniformly sensitive chloride of silver paper to the 

 action of its rays. Two registrations were carried out with each 

 light : first, paper was exposed to the naked light at a fixed 

 distance from the carbon points for three minutes ; and secondly, 

 a strip of the same paper was exposed beneath black wedges of 

 slight taper for sixteen minutes. The eye observations were 

 carried on simultaneously with the latter exposure of the sensitive 

 paper, in both cases obtaining an integration, as it were, of the 

 light during that period. Between ten and twenty observations 

 were taken for each light at the beginning, middle, and end of 

 each trial. Diagrams of the steam pressure were taken in the 

 usual manner, and diagrams were also taken of the steam 

 pressure when driving the machine without exciting a current, 

 at the same speed as that at which the light was produced. They 

 were also taken in many cases when the machines were what may 

 be called short circuited. The data were thus obtained for calcu- 

 lating the power necessary to produce a light of a certain value. 



Diagrams were exhibited showing the mean of the results of 

 a series of experiments with one instrument ; one curve, deduced 

 from eighty readings, giving what may be called the optical 

 value ; another, deduced from 450 readings, giving the actinic 

 value ; whilst a third showed the ratio of the actinic to the optic 

 value — the abscissa; being in all these cases measures of the 

 horse power. The curves are interesting as showing the rapid 

 decrease of the optical value, and still more of the actinic value, 

 of the light when worked with a low motive power. They also 

 show that each machine has a point beyond which the increase 

 in motive power is not compensated for by increase in light, the 

 curves apparently becoming asymptotic. 



Captain Abney stated that he was not at all prepared for the 

 great diminution of the value of actinic power in the lights, 

 though he expected it in a smaller degree. The early experi- 

 ments of Draper and others had shown that with increase of 

 temperature the more refrangible portions of the spectrum appear 

 after the least refrangible, but there seemed to be no measure- 

 ments which would have been applicable to the present set of 

 experiments. The curves must evidently be some function of the 

 wave-lengths, and the author hoped to carry out other experi- 

 ments in fixed portions of the spectrum in order to ascertain if 

 the formula whichjhe thought should hold good could be em- 

 ployed. 



SECTION B. 



Chemical Science. 



Opening Address by A. G. Vernon Harcourt, M.A., 

 F.R.S., F.C.S., President. 



To the privilege of presiding over this Section custom has 

 added the duty of offering some preliminary remarks upon the 

 branch of science for whose advancement we are met. 



In discharge of this duty some of my predecessors have re- 

 viewed the progress of chemistry during the previous year ; and 

 until a fcvf years ago there was no more needful service that your 

 President could render, though the task of selection and abstr-.c- 

 tion was one of ever-increasing difficulty. But a few years ago 

 the wisdom and energy of Dr. Williamson transformed the 

 Journal of the Chemical Society into a complete record of che- 

 mical research, and this Association materially promoted the 

 advancement of science when it helped the Chemical Society in 

 an undertaking which seemed at one time hopelessly beyond its 

 means. The excellent abstracts contributed to the Journal err, 

 if at all, on the side of brevity, and yet the yearly volume seems 

 to defy the bookbinder's press. I shall not venture to attempt 

 further abstraction, nor to put before you in any way so vast and 

 miscellaneous an aggregate of facts as the yearly increment of 

 chemistry has become. The advancement of our science — to 

 borrow again the well-chosen language of the founders of this 

 Association — is of two kinds. The first consists in the discovery 

 and co-ordination of new facts ; the second in the diffusion of 

 existing knowledge and the creation of an interest in the objects 

 and methods and results of scientific research. For the advance 

 of science is not to be measured only by the annual growth of 

 a scientific library, but by the living interest it excites and the 

 number and ardour of its votaries. The remarks I have to offer 

 you relate to the advancement of chemistry in both aspects. 



One fact has been brought into unpleasant prominence by the 

 Journal of the Chemical Society in its present form, namely, the 

 small proportion of original work in chemistry which is done in 



