50 



NATURE 



[November 8, 1900 



present carried on by educational bodies other than that 

 Ijoard." Examinations are held in India and in several of the 

 : colonies as well as at home. The report shows that Bombay 

 , sent up this year thirty-eight candidates in cotton manufacture 

 and dyeing, against eighteen last year. Earnest efforts are being 

 made to provide technical instruction for operatives engaged in 

 cotton mills in or near Bombay, and, with the further develop- 

 ment of the cotton industry, the number of candidates from 

 India who present themselves for the institute's examination is 

 likely to increase. 1 he work of the department also includes 

 the direction of instruction and the conduct of examinations in 

 technology and manual training. The instruction in manual 

 training is intended exclusively for those who are preparing to 

 become teachers in elementary or secondary schools. The 

 difficulty of arranging for the special instruction in the methods 

 of teaching, of which artisan students stand in need, has for 

 some time engaged the seriousattention of the institute, and, with 

 a view of indicating the kind of lessons which it was thought 

 desirable that County Councils might provide, a letter, enclosing 

 a suggested scheme of instruction, was addressed in November 

 last to the organising secretaries, and secretaries of local com- 

 mittees having manual training classes under their charge. 



SCIENTIFIC SERIAL. 



Bulletin of the American Mathematical Society, October. — 

 Prof. F. N. Cole gives an account of the proceedings at the 

 seventh summer meeting of the Society, which was held in June 

 last at Columbia University, New York City. The occasion 

 was one of the most successful in the Society's history, having 

 been attended by upwards of fifty members. Abstracts are given 

 of many of the papers read. These papers will subsequently 

 appear either in the Bulletin or in the Transactions. In con- 

 nection with this gathering, the final session was devoted to an 

 organised discussion of the following question : — What course 

 in mathematics shall be oflered to the student who desires to 

 devote one-half, one-third or one-fourth of his undergraduate 

 time to preparation for graduate work in mathematics? An 

 abstract of papers read by Profs. Moore, Harkness, Osgood, 

 Morley and Young is given by Prof. W. H. Maltbie. The 

 discussion suggests many points of interest. Prof. (Miss) C. A. 

 Scott furnishes an interesting article on a memoir by Riccardo 

 de Paolis. This mathematician about twenty years since pub- 

 lished a series of memoirs dealing with the (2, i) transformation 

 of the plane (cf. Atti d r. Accad. dei Lincei, vol. i. (1877) pp. 

 511-544; vol. ii. (1878) pp. 31-50 ; and pp. 851-878). An 

 exhaustive treatment is given, and Miss Scott ends thus : " the 

 intrinsic interest of de Paolis' work is surely excuse enough for 

 devoting some little space to it" in the Bulletin. References 

 are freely made to the writings of other geometers on cognate 

 lines. The " Notes " are full of the " Courses in Mathematics " 

 for the winter semester at most, if not all, of the German 

 Universities. Other details of interest to mathematicians fill up 

 the remainder of the number, together with a long list of recent 

 publications. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, June 21. — "Energy of Rontgen and Bec- 

 querel Rays and the Energy required to produce an Ion in 

 Gases," by E. Rutherford, M.A., B.Sc, Macdonald Professor 

 of Physics, and R. K. McClung, B. A., Demonstrator in Physics, 

 McGill University, Montreal. Communicated by Prof. J. J. 

 . Thomson, F.R.S. 



The primary object of the investigations described in the paper 

 was the determination of the energy required to produce a 

 gaseous ion when X rays pass through a gas, and to deduce from 

 the result the amount of energy radiated out into the gas by 

 uranium, thorium and the other radio-active substances. 



In order to determine this " ionic energy " it has been neces- 

 sary to accurately measure the heating effect of X rays and the 

 absorption of Rontgen radiation in passing through a gas. 



The method adopted to determine the ionic energy was briefly 

 as follows : — 



The maximum current between two electrodes produced by 

 the ionisation of a known volume of the gas by the rays was 

 determined. 



NO. 16 I 9, VOL. 63] 



In order to ionise the gas energy has to be absorbed, and the 

 intensity of the radiati( n talis ofif more rapidly than the law of 

 inverse squares. Assuming that the energy of the radiation 

 absorbed in the gas is expended in the production of ions, then, 

 knowing the coefficient of absorption of the rays in the gas, the 

 total current produced by the complete absorption of the whole 

 radiation given out by the bulb into the gas can be deduced. 

 Let i = maximum current produced by the total ionisation of 

 the gas by the rays, 

 n = total number of ions produced per sec, 

 * = charge on an ion. 

 Then i = ne. 



Let H = heating effect per sec. due to the rays when absorbed 

 in a metal, 

 E = total energy of the rays in ergs, 

 Then E = JH, where J = Joule's equivalent. 



If W = average energy required to produce an ion, then 

 mW = E = JH, 



... w = JiL=Jlif. 



n t ' 



The values of H and / are experimentally determined, and, 

 assuming the value of e, namely, 65 X io~'" electrostatic units, 

 determined by J. J. Thomson, the value of W is found in absolute 

 measure. 



Heating Effect of the Kays. 



An automatic focus tube was employed, excited by a large 

 induction coil with a special form of Wefinelt interrupter giving 

 57 breaks per second. The bulb gave out intense rays of a very 

 penetrating character. 



The heating effect was measured by determining the variation 

 of resistance in a specially constructed platinum bolometer when 

 the rays fell upon it. The heating effect was standardised by 

 observing the change of resistance caused by the passage of a 

 known current through the bolometer. Special precautions 

 were taken to screen oft all heating effects except that due to the 

 X-rays employed. 



About "55 of the incident rays were absorbed in the platinun^ 

 bolometer. The energy dissipated in exciting secondary radia- 

 tion at the surface of the platinum was neglected in comparison 

 with the total energy absorbed. 



The rate of supply of heat to the bolometer surface (area 92 '2 

 square cms. ) at a distance of 26 cms. from the source of the rays 

 was about 



o*oooi4 gramme-calorie per sec. 



The total energy of the rays given out from the front surface 

 of the platinum antikathode (omitting absorption of rays in glass 

 of bulb, air, and screens, &c.) was 



o"oii gramme-calorie per sec. 



Absorption of X-Rays in Gases. 



A null method was employed, as the absorption of the rays in 

 air at atmospheric pressure was small. The rays passed through 

 two long brass tubes with aluminium ends, and the current pro- 

 duced by the rays, after passing through one tube, was balanced 

 against the current due to the other. On exhausting one tube 

 the electrometer balance was disturbed. From measurements 

 of the deflection per second from the balance and the deflection 

 per second due to the rays after passing through one tube, the 

 absorption can be calculated. The mean value of the coefficient 

 of absorption of the rays in air at atmospheric pressure was found 

 to be 



0*000279, 



or the rays would pass through 247 metres before absorption 

 reduced the intensity of the radiation to one-half. 



The absorption was found to be proportional to the pressure 

 from a half atmosphere to three atmospheres. 



The coefficientjOf absorption in carbonic acid gas was found to 

 be I "59 times the absorption in air. 



Energy required to produce an Ion. 



The current produced when a given volume of the gas vras 

 ionised by X rays was determined by means of an electrometer. 

 In order to get rid of the secondary radiations set up when X 

 rays strike on a conductor, the rays passed between two charged 

 parallel plates without striking them. A guard-ring method 

 was employed to ensure uniformity of the electric field. 



The value of the ionic energy was deduced from the deter, 

 mination of the current, heating effect and absorption of the 



