May 9, 1907J 



NA TURE 



41 



instead of the value 587 generally accepted by chemists. 

 This result, which is confirmed in a letter just received 

 from Prof. B. Walter, of Hamburg, is based on the law 

 that the secondary Rontgen rays from a chemical element 

 have a specially high penetrative power with regard to 

 the material from which they originate ; for other, elements 

 this specific penetrative power falls off proportionately as 

 the atomic weight of the element differs from that of the 

 substance producing the rays. Prof. Walter points out, 

 however, that the general properties utilised by Mr. Barkla 

 as a basis for his considerations were in the main pub- 

 lished by him in the year 1905 (,.\nna\en dcr Physih, 

 Bd. 17. p. 561 ; Fortschritte aiif dem Gebiete der Rontgen- 

 strahleii, Bd. 8, p. 297). Referring to the fact that .Mr. 

 Barkla does not accept a specific power of penetration such 

 as Prof. Walter suggested, but holds the opinion which 

 was generally accepted previously, that a selective absorp- 

 tion takes place, Prof. Walter says that this assumption 

 is shown in his papers to lead to contradictions in the case 

 of the primary Rontgen rays. In his opinion, it cannot 

 be correct in the case of the secondary rays, because the 

 phenomena in question become all the more apparent for 

 these rays the thinner the absorbing laminse be made. 

 .According to Mr. Barkla 's conception, exactly the opposite 

 should be true. 



Whilst cuprous chloride and bromide have long been 

 known, the existence of cuprous sulphate has been recog- 

 nised mainly as a disturbing factor in the copper volta- 

 meter. Owing to the formation of this salt, the copper 

 deposited on the kathode is liable to be partially re- 

 dissolved Cu-|-CuSO,Z^Cu„SOj, causing the deposit to be 

 too light : on the other hand, if the cupric solution has 

 been saturated with metallic copper, the deposit is too 

 heavy, since twice as much copper is deposited per coulomb 

 from the cuprous as from the cupric salt. The recent 

 experiments of Foerster and Blankenberg (Berichte, xxxix., 

 442S-4436) have added much to our knowledge of this salt. 

 By enclosing ammonium cupric sulphate with metallic 

 copper in sealed tubes they were able to ensure the form- 

 ation of a large proportion of cuprous sulphate, and 

 actually succeeded in isolating a double salt of the formula 

 Cu,SOj,4NH3,H,0. When quite dry, the salt can be 

 kept for some weeks in sealed tubes, but it is immediately 

 decomposed by dilute sulphuric acid, giving rise to metallic 

 copper and cupric sulphate. It is of interest to note that 

 a solution containing initially 0-05 mol. CuSO,, 0-95 mol. 

 NHj, and 0-15 mol. (NH|)„SOj, became quite colourless 

 wh^n saturated with metallic copper, and when electro- 

 lysed gave a kathode deposit 55 per cent, greater than 

 that obtained from a cupric solution in series. 



A POPULAR article upon the planet Saturn and its system, 

 by Mr. E. V. Heward, appears in the May number of the 

 Fortnightly Review. 



Excellent work is being done by the Central Technical 

 College Old Students' .Association, the official organ of 

 which, the Central, forms a very creditable addition to 

 periodical engineering literature. In the current issue 

 (vol. iv.. No. 11) there are original articles on the con- 

 struction of a new railway, by Mr. .A. C. Cookson, and 

 I on electrical test-shop' measurements, by Mr. Percy Good. 



We have received from Mr. C. Baker, of High Holborn, 

 London, an advance proof of his new quarterly catalogue 

 of second-hand scientific apparatus. The list contains 

 particulars of more than a thousand separate items, and is 

 worth examination. 



NO. 1958, VOL. 76] 



OUR ASTRONOMICAL COLUMN. 

 C0.MET 1907a (Gi,\coBixi).-^\o. 4173 (p. 336, April 27) 

 of the Astronomische Nachrichtcn contains a new set of 

 elements for comet 1907a, computed by Miss Lamson, in 

 which the time of perihelion passage is given as 

 March 17.66. A daily ephemeris, calculated bv Prof. 

 Kreutz and based on these elements, is also given, and 

 extends to May 22. The comet is at present apparently 

 travelling very slowly and nearly due north in the northern 

 limits of Orion, its computed positions for May g and 

 May 22 respectively being a = hh. iim., 5 = 4-14° 7'-4 and 

 a = 6h. 14m., 5=4-17° 5'.8. The brightness of this object 

 is now about one-quarter of that at the time of discovery, 

 when it was of the eleventh magnitude. 



The Temperature oi-* tue Sun. — An excellent popular 

 description of the apparatus and methods by which MM. 

 Millochau and F^ry determined the solar temperature 

 during 1906 is given by the former observer in La Nature 

 (No. 1770, p. 338, April 27). As previously recorded in 

 these columns (see Nature, No. 1932, p. 40, November S, 

 1906), the observations were made at Meudon, Chamonix, 

 the Grands Mulcts, and the summit of Mont Blanc during 

 July and August last. The instrument used was the 

 pyrheliometric telescope devised by M. F^ry in 1902, and 

 described and illustrated in the paper under notice. 

 Essentially it consists of a reflecting telescope, having a 

 mirror of 103 mm. diameter and 80 cm. focal length, in 

 the focus of which is placed a thermoelectric couple, which 

 is connected with a galvanometer reading directly to about 

 one-hundredth of a millivolt. The couple is composed of 

 two wires, one of iron, the other of constantan, soldered 

 together .at their point of intersection, the joint being 

 covered with a carefully blackened, very small and very 

 light disc. .A bent eye-piece, placed behind the reticule 

 bearing the couple, enables the observer to direct the 

 telescope to any desired portion of the solar disc. The 

 results obtained gave a temperature of 5663°, absolute, for 

 the centre of the solar disc, considering the sun as an 

 ideal black body, or, as M. Guillaume terms it, an 

 " integral radiator." Correcting this value for the prob- 

 able absorption in the solar atmosphere, M. Millochau 

 obtains 6130° absolute as the effective temperature of the 

 sun's interior. 



Photography of the Infra-red Solar Spectrum. — In 

 No. 14 (p. 725, April 8) of the Comptes rendus M. Millo- 

 chau records some results he has obtained in the photo- 

 graphy of the infra-red region of the solar spectrum. The 

 plates employed were specially prepared by plunging them 

 for about ten minutes into distilled water to which several 

 drops of acetic acid had been added, then into a saturated 

 alcoholic solution of malachite green, and finally washing 

 and drying them. They were then rendered much more 

 sensitive by exposing them for 30 seconds at a distance 

 of 75 cm. to a 4 candle-power electric lamp, according to 

 the method suggested by Major-General Waterhouse in 



With plates thus prepared the solar spectrum was 

 photographed, in ^the region 0-750 n to 0-950 /t, on such 

 a scale that one Angstrom unit = 0-1 mm., the photographs 

 showing that the structure of the A band in the solar 

 spectrum is identical with that of the B band. Another 

 photograph showed the Z band resolved into lines. 



.A plane-grating spectrograph of 3 cm. aperture and 

 60 cm. focal length was employed, and with this apparatus 

 the A band, under good conditions, could be photographed 

 in ten, and the e.vtreme region in thirty, minutes. 



The Orbit of o Duaconis. — The following elements 

 have been found for the orbit of a Draconis from spectro- 

 grams secured at the Dominion Observatory, Ottawa, by 

 Mr. J. S. Plaskctt : — period = 5i-42 days, € = 0.322, w = 

 20°.3, nj„ = 294°, T=i9o6 July iid. 4h., velocity of 

 system = — iS-4 kin. per sec. 



In No. 2, vol. i. (March-.April) of the Journal of the 

 R..A.S. Canada, where the above is published, Mr. Plaskett 

 also gives a very interesting description of the methods 

 employed in adapting a Brashear universal spectroscope to 

 the requirements of line-of-sight spectrography. 



