November 28, 1895] 



NATURE 



95 



theory that the two gases are really separated by diffusion. 

 Three of the original negatives taken by Prof. Rowland when 

 piejiaring his map of the solar spectrum were also exhibited. Dr. 

 ( iliidstone said he had examined the spectrum of the gas in two 

 ;iil)es, one of which had been filled by diftusion through an 

 ushestos plug, and the helium line (D3) was certainly brighter in 

 (Uie tulje than in the other, though the brightness of the remain- 

 int^ lines appeared about the same in both tubes. As to the 

 (li'rticulty of allocating the new gases in Mendelejeffs table, it 

 appeared to him (Dr. CHadstone) that they would have to be put in 

 the first group between hydrogen and lithium. An examination 

 of the successive differences between the atomic weights of ad- 

 jacent members of the metals in the first group showed that these 

 differences increased as we go downwards. If then the new 

 gases have atomic weights of, say, 2 and 4, we should have for 

 these differences 2, 2, 3, 16, 16, 26, &c., instead of 6, 16, 16, 

 &c.,asat present. The important point which required investi- 

 gation was whether these two gases were really simple bodies or 

 not. Prof. Silvanus Thompson asked if Runge and Paschen 

 had performed a similar analysis of the lines in the spectra of 

 other elements besides the members of the first group. He 

 would also like to know if in the case of any element besides 

 hydrogen the lines could be arranged in a single series. Dr. 

 Stoney, in reply, said that the spectra of most of the metals had 

 been analysed, the chief exceptions being iron, nickel, 

 cobalt, and manganese. There was no other element 

 besides hydrogen which gave a single series of lines. 

 Prof. Herschel gave an account of a line of reasoning 

 which had led him many years ago to a formula resembling that 

 expressing Balmer's law for the hydrogen lines, namely, 

 i= I -4. The Chairman (Captain Abney) drew attention to the 



fact that Runge expressed his result to i/ioooth of an Angstrom 

 unit, although. Dr. Stoney had said the measurements could only 

 be made to within i/50th of a unit. There was great lack of 

 unifonnity in the method of drawing spectra in general use ; he 

 strongly recommended the placing of the red end of the spectrum 

 to the right, so that the wave-lengths increased from left to 

 right. As to the three series of lines obtained in the case of most 

 elements, it was not conclusively proved that they were not due 

 in each case to three distinct kinds of molecules, and it will 

 probably be found that there are more than two simple gases 

 present in the gas evolved from cleveite.— Mr. R. Appleyard 

 read a note on the action of sulphur vapour on copper. When 

 a copper wire is exposed for some time to the action of sulphur 

 vapour, it becomes entirely converted into sulphide of copper, 

 and it is found that there is a fine axial hole running down the 

 rod of sulphide formed. Rods of copper of square section cut 

 from a block of copper after exposure to the action of sulphur 

 vapour also exhibited the axial hole, the rod of sulphide formed 

 being of circular cross-section. In every case the diameter of 

 the rod of sulphide is about twice that of the origmal 

 ro<l of copper. Delta metal was found to be unacted upon by 

 the sulphur vapour.— Mr. Appleyard then read a paper on a 

 " direct -reading " platinum thermometer. This form of platinum 

 thermometer has been devised with the view of determining the 

 temperature of the dielectrics employed in some experiments on 

 the variation of the electrical resistance of dielectrics with tem- 

 perature. The thermometers consist of six platinum coils, each 

 of about seven ohms resistance, attached to thick copper leads. 

 A slide-wire Wheatstone's bridge is employed to measure the 

 resistance. The stretched wire is three metres long, and the 

 moving contact so arranged that it is impossible to damage the 

 wire. The auxiliary coils used in connection with the bridge are 

 immersed in a bath of paraffin oil, the temperature of which is 

 maintained constant, and a little above that of the air, by means 

 of a glow-lamp immersed in the oil. Mr. Appleyard also read 

 a historical note on resistance and its change with temperature, 

 in which he showed that the earliest measurements of the 

 variation of resistance with temperature were made by Lentz m 

 1833. Some experiments on this subject made by Davy were 

 also referred to, and some of these experiments repeated 

 before the Society. Mr. Trotter said he agreed with the author, 

 that the " reserve of precision " at our disposal, on account of the 

 delicacy of some of the modern instruments, ought to be made 

 use of to facilitate the rapid performance of many measurenients 



where the utmost accuracy is not necessary. 



He had the 



...ipression that platinum silver was not now considered the best 

 material for use as the bridge wire. Mr. II. F. Burstall 

 explained the differences between the temperature as measured 



NO. I 36 1, VOL. 53] 



on the mercury, air and platinum thermometers. At a temperature 

 of about 40° the platinum thermometer read about o°"4, and the 

 mercury thermometer about o°'l below the air thermometer. 

 Prof. Callendar had obtained measurements of temperature 

 correct to within o"*! by using a Weston voltmeter and an 

 ordinary Wheatstone bridge the variations of resistance, and 

 hence the temperature being read directly from the deflections 

 on the voltmeter. Mr. Rhodes thought that, except where 

 extreme accuracy was necessary, the mercury thermometer was 

 very much more convenient than the platinum thermometer. 

 Mr. Burstall said the great convenience of the platinum thermo- 

 meter lay in the fact that the scale could be read at a distance of 

 many yards from the point where the temperature was being 

 measured, and hence could be used in many places where it 

 would be impossible to read a mercury thermometer. Mr. 

 Blakesley considered that the author was somewhat bold to state 

 that for general purposes it was never necessary to measure 

 temperature to nearer than one-tenth of a degree. The author 

 having replied, the Society adjourned till December 13. 



Mathematical Society, November 14. — Major MacMahon, 

 R.A., F.R.S., President, in the chair. — The President an- 

 nounced the death of Mr. E. H. Rhodes (elected June 10, 1875), 

 which took place on the ist inst — The gentlemen, whose names 

 were published in Nature of October 31, were, after the ballot 

 had been taken, declared duly elected on the Council for the 

 ensuing session. — The President stated the reasons which had 

 led Mr. M. Jenkins, after thirty years' tenure of the office, to 

 resign his position of Secretary, and moved a vote of thanks to 

 that gentleman for his" devoted services of thirty years" to the 

 Society, and coupled with the vote the hope that his health 

 might be improved by his retirement to the country. The vote 

 was seconded by Mr. Kempe, F.R.S., and supported by Mr. S. 

 Roberts, F.R.S., who had been connected with the Society 

 almost from its inception. After the vote had*)een unanimously 

 carried, Mr. Jenkins suitably thanked the Society and the 

 speakers for their good wishes and appreciation of his services. 

 The following papers were read or communicated : On the 

 stability and instability of certain fluid motions (iii.), and on the 

 propagation of waves upon the plane surface sei-»arating two 

 portions of fluid of different vorticities, by Lord Rayleigh, Sec. 

 R.S. The two earlier papers upon the subject of these com- 

 munications are to be found in the Society's Proceedings (\o\. xi., 

 1880, and vol. xix., 1887).— Determination of the volumes of 

 certain species of tetrahedron without employment of the method 

 of limits, by Prof. M. J. M. Hill, F.R.S. Proofs are first given 

 of the propositions : (A) that it can be shown without dissection 

 that symmetrically equal tetrahedra are equal in volume. (B> 

 That two tetrahedra having a common base, and being the 

 images of one another with regard to that base, are equal. (C) 

 That a tetrahedron, in which the line joining the middle points 

 of two opposite edges is perpendicular to those edges, can be 

 bisected into two superposable tetrahedra by a plane through 

 either of these edges and the middle point of the other. By 

 means of (B) a tetrahedron of special form is constructed, such 

 that a prism can be built up of this tetrahedron and two of its 

 successive images. The volume of this species of tetrahedron is 

 then known without employment of the method of lim.ts. Call- 

 ing it ABCD, its sides are expressible in terms of two para- 

 meters a, r as follows : 



AC = a V9 - 3^2, AD = BC = 2a, 

 AB = BD = DC = « Vi -f r*. 

 By means of (C) two other types of tetrahedra, whose sides are 

 expressible in terms of two parameters, are deduced from the 

 tetrahedron ABCD. Also by a consideration of a special case 

 of the tetrahedron ABCD, the volumes of two tetrahedra of 

 definite shape, not included in the above-mentioned types, are 

 determined.— An extension of Sylvester's constructive theory of 

 partitions, by the President. In connection with this paper the 

 President communicated a paper by Prof. Forsyth, F.RS., 

 entitled, " Some algebraic theorems connected with the theory of 

 partitions.' The f<aper is concerned with a general method lead- 

 ing to the proof of some theorems required in Major MacMahon's 

 investigations in the partitions of numbers. They depend upon 

 the summation of terms selected from the series, which is the 

 expansion of particular fractions, and the summation is effected 

 algebraically.— On the evaluation of a certain dialytic deter- 

 minant, by Mr. W. W. Taylor. In a jjaper read before the 

 Society in March 1894, Prof. Elliott (the author) remarked : " It 



