June 24 1909J 



NA TURE 



509 



and the committee of the Leather Trades School. It 

 includes also the address delivered last January at the 

 annual distribution of prizes by Mr. Gerald Balfour. The 

 report of the council summarises the growth in the recent 

 activities of the institute, and provides a clear statement 

 of the precise relations of the Central Technical College 

 with the Imperial College of Science and Technology and 

 with the University of London. The report of the Depart- 

 ment of Technology shows convincingly the great extent 

 of the work accomplished by the institute in the direction 

 of improving and extending the facilities for technical 

 instruction throughout the country. During the session 

 under review, that for 1907-8, 3604 classes were registered 

 in one or other of the seventy-six different subjects in 

 technology included in the institute's programme. These 

 classes were held at 402 centres in 299 towns, and were 

 attended by 48,223 students, or 2175 more than in the 

 previous session. There are, it appears, two main causes 

 which impede progress in the technical instruction of 

 artisans ; first, there is the difficulty of finding competent 

 teachers, and, secondly, the unduly large proportion of 

 artisan students who enter technical classes without the 

 preliminary knowledge necessary to take full advantage of 

 the instruction they receive. The report points out at the 

 same time that there is no doubt that the teaching of 

 technology has improved greatly during the past decade, 

 and it is satisfactory to find that there is no relaxation of 

 effort on the part of the institute to raise the standard 

 of work in the classes under its care. 



SOCIETIES AND ACADEMIES. 

 London. 

 Physical Society, June 11. — Dr. C. Chree, F.R.S., presi- 

 dent, in the chair. — The Arthur Wright electrical device 

 for evaluating formula and solving equations : Dr. Russell 

 and Arthur Wright. Special slide resistances are used. 

 If R be the resistance of one of these, and a metallic 

 finger make contact with it at a point where the scale- 

 reading is .V, the resistance between this finger and the 

 terminal of the slide is R/x. The scales are graduated 

 as in the ordinary slide-rule. If a number of these slide 

 resistances be connected in parallel, the sum of the currents 

 through them will be proportional to the sum of the read- 

 ings of the contact fingers. By a null method this current 

 can be balanced against the current going through a 

 single slide resistance X by means of a VVheatstone's 

 bridge arrangement. The reading on X when there is a 

 balance gives the sum of the readings on all the other 

 slides. Similarly, numbers can be subtracted by putting 

 slides representing these numbers in parallel with X, and 

 then obtaining a balance by altering the reading on X. 

 By clamping the contact fingers inclined at certain angles 

 to a rod which can be moved at right angles to the slides, 

 it is easy to obtain the values on X of f(_x) when 



J{x) = ax'" + dx" -,- ex'' + . . . , 

 where the indices )i>, n, p, . . . may be positive, negative, 

 or fractional, and the coefficients may be positive or 

 negative numbers. A model of this device for solving an 

 equation of any degree consisting of not more than four 

 terms was shown. The inaccuracy of the results found 

 by means of this model is of the order of i per cent. 

 .Approximate values of the imaginary roots of numerical 

 equations can be found by the device, which can be 

 employed also to solve very complicated equations. — The 

 echelon spectroscope, its secondary action and the struc- 

 ture of the green mercury line : H. Stansfield. An 

 investigation of the action of an echelon spectroscope and 

 the results obtained as to the structure of the green 

 mercury line given by an Arons lamp. The echelon 

 spectroscope employed was arranged so that the auxiliary 

 prism could be mounted next to the echelon. The dis- 

 persion of the prism may be added to or subtracted from 

 the dispersion of the echelon, and the change in the dis- 

 persion obtained gives a method of determining whether 

 two lines in the spectrum belong to the same order. Fabry 

 and Perot spectra are produced by the secondary action 

 of the echelon. When the echelon is tilted the secondary 

 light may be separated from the primary, and parts of 

 the Fabry and Perot circles observed with a wide slit. 



The secondary light also undergoes the primary echelon 

 treatment, and, with a narrow slit, is confined to the 

 points of intersection of the two systems of spectra. 

 When the echelon is in the ordinary position the secondary 

 spectra are lines similar to the primary echelon lines, and 

 may be observed moving across the broad central line 

 when the echelon table is rotated slowly. — The proposed 

 international unit of candle-power : C. C. Paterson. The 

 paper discusses the units of candle-power at present 

 officially accepted in Great Britain, France, the United 

 States of America, and Germany. The authorities in the 

 gas and electric interests in the United States are pre- 

 pared to adjust their units of candle-power to bring them 

 to a single value, which is to be the same as the British 

 and French units. The paper gives the results of com- 

 parisons showing that, within the limits of experimental 

 error, the British and French units are identical. The 

 change involved in the unit maintained at the Bureau of 

 Standards, Washington, is 1-6 per cent. The Hefner unit 

 is almost exactly nine-tenths of the new unit. — Inductance 

 and resistance in telephone and other circuits : Dr. J. W. 

 Nicholson. A general formula for the effective inductance 

 of a circuit consisting of two long parallel wires has been 

 given previously, and is suitable for cases in which the 

 current distribution in either wire is affected greatly by 

 the frequency of alternation. Important cases are 

 examined in detail here, and formulfe are obtained capable 

 of immediate use. A calculation of the effective resistance 

 is also made in each case. Throughout the investigation 

 only iron and copper wires as the two extreme cases are 

 considered. The large permeability of iron completely 

 changes the character of the effect of frequency on its 

 self-induction. To all metals greatly used in practice, 

 e.xcept iron, the formulae developed for copper wires may 

 be applied with a nearly identical order of accuracy. — 

 Note on terrestrial magnetism : G. W. Walker. — The form 

 of the pulses constituting full radiation or white light : 

 .A. Eagrle. 



Paris. 



Academy of Sciences, June 14. — M. Bouchard in the 

 chair. — Some remarks on integral equations of the first 

 species, and on certain problems of physical mathematics ; 

 Lmile Picard. — Some earthquakes which have devastated 

 Provence and Dauphin<5 : G. Bigourdan. .A chronological 

 list of the earthquakes on record as happening in these 

 districts between 1282 and 1812. — Presentation of three 

 new sheets of the map of the edible molluscs of the coasts 

 of France, established by M. Joubin : the Prince of 

 Monaco. — Observations of the sun made at the Lyons 

 Observatory during the first quarter of igog ; J. 

 Guillaume. Observations were made on forty-four days 

 during the quarter ; the results are summarised in three 

 tables, showing the number of spots, their distribution in 

 latitude, and the distribution of the faculs in latitude. — 

 The latitude of the Observatory of Athens : D. Eginitis. 

 A discussion of the cause of a systematic error of about 

 1.26" in the meridian-circle readings. — Observation of the 

 total eclipse of the moon of June 3, 1909, at the Observa- 

 tory of Toulouse : L. Montangerand. A special photo- 

 graphic study of totality. — The pseudo-elliptic or hyper- 



' p rV.r 



elliptic integrals of the form / - " : E. Vallier. 



— A recent note of M. S. Bernstein : S. Zaremba. — • 

 Differential equations with fixed critical points : J. Chazy. 

 — The study of the variations of statistical quantities : 

 Emile Borel. — A law permitting the immediate calculatior> 

 of the approximate profile of a watercourse of given flow 

 when the section of the liquid and the wetted perimeter 

 are algebraic functions of the height of the water : Philippe 

 Bunau-Varilla. — The condensation of the radium emana- 

 tion : A. Laborde. After condensing the emanation by 

 cooling in tubes of copper, iron, tin, silver, glass, and 

 silvered glass, the temperature at which the emanation 

 was evolved was measured, and was found to be —153° C. 

 to -155° C. for the four metals, -175° to -179° in 

 glass. The absorptive properties of meerschaum, charcoal, 

 platinum black, and spongy platinum for the emanation 

 were also studied. — A new wave detector for wireless tele- 

 graphy and telephony : G. E. Petit. The detector consists 



NO. 2o6g, VOL. 80] 



