October 12, ign] 



NATURE 



General Physics. 



In the department of general physics Mr. N. E. Dorsey 

 gave an account of the work done at the Bureau of 

 Standards on the absolute measurement of electric current. 

 The measurements were made with a balance of the Ray- 

 leigh type ; the coils were wound bifilarly, of enamel- 

 insulated wire, upon brass forms. A novel feature of the 

 fixed coils is the provision, in the forms and back of the 

 windings, of a channel, through which water can be 

 pumped so as to maintain the coils at a constant tempera- 

 ture. A double-walled jacket with water circulation sur- 

 rounded the movable coils for the same purpose. The 

 mean value obtained of the electromotive force of the mean 

 Weston normal cell (as defined at the Washington con- 

 ference) at 20° C. in terms of the international ohm and 

 the Bureau balances is i-oiS22, twith a mean deviation of 

 9x10-'), which is 4 in 100,000 higher than the value 

 obtained at the National Physical Laboratory. The cause 

 of the discrepancy is not settled. 



Prof. F. T. Trouton followed with a paper on peculiari- 

 ties in the adsorption of salts by silica. Starting with 

 very dilute solutions and gradually increasing their 

 strengths, the smount of salt adsorbed first increases fast, 

 then more slowly (or even decreases), then more quickly 

 again. The thickness of the layer which exhibits the 

 anomaly is calculated as being comparable with the usually 

 giv-pn value for the range of molecular forces. 



Dr. J. W. Nicholson contributed a paper on the 

 atomic structure of the elements, with theoretical deter- 

 minations of their atomic weights, in which ?n attempt 

 was made to build up all the elementary atoms out of 

 four protyles containing, respectively, 2, 3, 4, and 5 elec- 

 trons in a volume distribution of positive electricity. 

 Representing the protyles by the symbols Cn (coronium), 

 H (hydrogen). Nu (nebulium), Pf (protofluorine), the 

 accompanying table indicates the deductions of the author 

 with regard to the composition of several elements, allow- 

 ance being made for the mass both of the positive and 

 negative electrons. 



The coincidence between the calculated and observed 

 values is very great, but the general attitude of those 

 present seemed to be one of judicial pause pending the 

 fuller presentation of the paper, stress being laid on the 

 fact that any true scheme must ultimately give a satis- 

 factory account of spectra. The rest of the morning was 

 occupied with the reading of the reports of the committee 

 for establishing a solar observatory in Australia and the 

 committee on magnetic observations at Falmouth Observa- 

 tory. 



Prof. F. R. Watson contributed the results of experi- 

 ments undertaken in connection with curing the echoes and 

 reverberations in the auditorium at the University of 

 Illinois. In accordance with theory, it is found that a 

 broad sheet of warm air drawn over the head of the 

 speaker and out at the rear of the auditorium acts as a 

 partition, and more or less reflects and refracts the 

 speaker's utterances to the audience. In the absence of 

 the author, a paper by Mr. J. W. Gordon describing an 

 ingenious new micrometer was taken as read. 



Mr. W. H. F. Murdoch gave an exhibition and de- 

 scription of a friction permeameter. This is a develop- 

 ment of one previously designed by the author. In the 

 new form the defects of the old form are removed. Dr. 

 J. A. Harker followed with a paper (by himself and Mr. 

 W. F. Higgins) on the methods and apparatus used in 

 petroleum testing. He stated that it is well known that 

 the Abel-Pensky apparatus gives a higher result for the 

 same oil than the Abel. The results of experiments made 



NO. 2189, VOL. 8/] 



at the National Physical Laboratory by the authors show 

 that large differences of temperature exist throughout the 

 oil cup and vapour space above it at any stage during an 

 experiment amounting to 5^ F. or more, and they are 

 different in the different types of apparatus. The size of 

 the test flame is also shown to be of importance. The 

 difference of temperature in the two types is found to be 

 due to the cover in the Abel-Pensky form containing much 

 more metal, and therefore requiring longer to warm up. 



The proceedings on Monday, September 4, began with a 

 joint discussion with Section G on mechanical flight. A 

 special article on this discussion has appeared elsewhere in 

 this journal, and consequently it will not be further men- 

 tioned here. 



Corpuscular Radiation. 



A discussion was opened by an extremely lucid and 

 persuasive paper by Prof. W. H. Bragg on corpuscular 

 radiation. Such radiation he denned as consisting of 

 entities or " quanta " each moving in a straight line with 

 uniform velocity and unchanging properties unless impressed 

 forces cause a change. The a and /3 rays are corpuscular, 

 but not sound or light as ordinarily conceived. With regard 

 to X (and 7) rays, it must be observed that the speed and 

 direction of a ray produced by an X-ray depend on the 

 quality of the- X-ray and not on the nature of the atom. 

 The energy of the J3 ray, therefore, cannot come from the 

 atom ; nor yet can it be the result of the accumulation 

 in the atom of energy extracted from many X-rays, for it 

 can hardly be supposed that the accession of the last 

 infinitesimal amount of energy required would determine 

 so effectively the direction in which the & ray is ejected. 

 Therefore one X-ray provides the energy for one j8 ray, 

 and vice versa, and Whiddington's results show that very 

 little energy is lost in the transformation. Again, since 

 the speed of the secondary /3 ray is independent of the 

 distance which the X-ray has travelled, the latter cannot 

 diffuse its energy as it proceeds. Again, X-rays can excite 

 X-ravs of less, but not greater, penetrating power than 

 themselves ; and they must have arisen from 3 rays of 

 energv exceeding a certain limit, viz. that characteristic of 

 the X-corpuscle of that substance. The spreading pulse of 

 Stokes and the kink in a tube of force (Thomson) fail to 

 account for these facts ; only a corpuscular theory will do 

 this. Prof. Bragg's working model of such a corpuscle is 

 a " neutral pair." 



Sir Wm. Ramsay in the ensuing discussion asked 

 whether a similar explanation might not account for the 

 sun remaining hot so long, assuming it only sends out 

 radiations in the directions for w-hich a body exists to 

 receive them. He also directed attention to experiments of 

 his own in which radium enclosed in a glass tube sur- 

 rounded by a second vessel gradually excited radio-activity 

 in the latter. If the outer vessel is dissolved, an active 

 [ substance can be chemically precipitated. His own theory 

 is that the 3 rays shot out from the radium excite an 

 actual chemical change in which a radio-active substance 

 is produced. 



Dr. Lindemann suggested that a crucial test between 

 corpuscular and wave theory is supplied by the value of 

 radiation pressure being twice as great on the corpuscular 

 theory, but the reply came that the pressure is too small 

 to be measured at present. Pulses of genuine delight ran 

 through the meeting while Prof. Bragg expounded his 

 views, and it was clear that many were impressed by the 

 cogency of his arguments. 



In a paper on the dependence of the spectrum of an 

 element on its atomic weight. Prof. W. M. Hicks showed 

 how to represent by formulae the lines of a spectrum which 

 are related to the well-known series in the same way as 

 the second or third set of a doublet or triplet series depends 

 on the first, or as the satellite lines of a D series depend 

 on the more intense set. Examples were given from the 

 sharp series of Mg, Ca, and Sr, but the other series show 

 similar connections. In the absence of Major E. H. Hills 

 a paper by him on the arc spectra of certain metals in the 

 infra-red (\ 7600 to X 10,000) was taken as read. This 

 paper details the results of measurements made on photo- 

 graphic plates coated with a collodio-bromide emulsion, as 

 originally used by Abney in 1880. Measurements by others 

 have usually been made with a thermopile or bolometer. 



Dr. Harker read a paper, on behalf of Mr. H. C. Green- 



