474 



NATURE 



[August 14, 1919 



three optical glass factories in operation, the supplies 

 were more than adequate for their domestic require- 

 ments. The output increased from 4000 kilos, a month 

 in 1914 to 12,000 in 1918. The claim advanced in the 

 article that this represents 80 per cent, of the total 

 Allied production can scarcely be correct, as our own 

 output during 1918 probably exceeded 9000 kilos, a 

 month. Like ourselves, France was largely dependent 

 before the war on German sources for supplies of the 

 higher grades of optical instruments. She is deter- 

 mined that this position shall not recur, and has 

 taken steps not only to safeguard her own supplies, 

 but also to secure a share of the world market. As a 

 means to this end, the Institut d'Optique, providing 

 for higher instruction in optics, research and testing 

 laboratories,- as well as for the training of skilled 

 glass workers and mechanics, has been founded. As 

 the head of the institute she has been fortunate enough 

 to secure Prof. Fabrv, for whom it is proposed to 

 create a chair of optics at the Sorbonne. The insti- 

 tute aims at fulfilling for the whole French optical 

 industry the functions which, in Germany, the special 

 technical staffs exercise for their own firms. The 

 institute will receive annual subsidies from the Minis- 

 tries interested in its work. 



The question is frequently raised in connection with 

 the use of aluminium and its alloys whether they can 

 be satisfactorily soldered ; and, if so, by what method 

 and with what metals and alloys. Aluminium and, 

 to a less extent, its alloys can be welded quite satis- 

 factorily by the oxygen-gas process, but often it is 

 not desirable to heat the parts to be joined to the 

 relatively high temperature necessary to weld them in 

 this manner, owing to the resultant distortion of the 

 parts, and a means of joining it at lower temperatures 

 is sought. The U.S. Bureau of Standards accordingly, 

 in its Circular No. 78, gives an account of special 

 tests recently made at the Bureau to determine the 

 general trustworthiness of aluminium solders. The 

 most common of these consist of tin as a base, with 

 the addition of zinc and aluminium, and sometimes 

 lead, "in moderate proportions. These metals and their 

 combinations are electrolytically electro-negative to 

 aluminium. A soldered joint is, therefore, rapidly 

 attacked and disintegrated when exposed to moisture. 

 There is no solder of aluminium of which this is not 

 true. Such joints should, therefore, never be made 

 unless they are to be protected against corrosion by 

 paint or varnish. Solders are best applied without a 

 flux after a preliminary cleaning and tinning of the 

 surfaces to be soldered. The composition rnay be 

 varied within wide limits. It should, consist of a tin 

 base with the addition of zinc or both zinc and 

 aluminium, the chief function of which is to produce 

 a semi-fluid mixture within the range of soldering 

 temperatures. The tensile strength of a good 

 aluminium solder is about 7000 lb. per sq. in. There 

 is no reason why it need be brittle, as several coni- 

 mercial varieties are, and it is very undesirable that it 

 should be. Its strength depends upon the type and 

 workmanship. 



In consequence of the increased cost of production, 

 the published prices of the Observatory and the Com- 

 panion are to be raised to t.<>. 6d. and 2s. 6d. respec- 

 tively, beginning with the new volume. 



The Wireless Press, Ltd., will shortly begin the 

 publication of a new monthly periodical entitled the 

 Radio Review, which will be devoted to the scientific 

 development of radio-communication and contain a 

 review of all current wireless literature. 



NO. 2598, VOL. 103] 



OUR ASTRONOMICAL COLUMN. 



Kopff's Periodic Comet (1906 IV.).— This comet, 

 an obser\'ation of which by Dr. Wolf was announced 

 last week, has since been photographed at Algiers en 

 August 4, and at Greenwich on August 6 and 7. In 

 default of an ephemeris, an approximate place for a 

 few days may be inferred from these observations : — 



G.M.T. {t..\. S. Decl. 



h. h. m. s. o / 



July 30 ... 10 19 27 12 9 32 



August 4 . . 10 19 26 32 9 57 



6 ... IO-6 19 26 24 8 57-1 



7 ... 10-6 19 26 23 8 53-2 



The comet was said to be of magnitude 105 on 

 July 30, and ii-o on August 7. 



Magnitude of Nova Aquil^.— The Astrophysical 

 Journal for June contains a series of measures of the 

 brightness of this star made by Mr. Stebbins and Mr. 

 E Dershem with the photo-electric photometer between 

 June 9 and December 10 of last year, on seventv-eight 

 nights in all. Noting the precision of the instrument, 

 for the probable error of one observation is said to 

 be of the order of a hundredth of a magnitude, this 

 series might be accepted as standard. It shows an 

 almost uniform decrease in the light of the star until 

 June 30 to mag. 3-3. There was an increase of 02 mag. 

 between the nights of July i and 3, a similar increase 

 between July 22 and 27, and an outburst measured 

 by 07 mag. between August 5 and 6. Later dates 

 when the brightness increased were September 1-5 

 (04 mag.), September 19-21 (02 mag.), October 6-12 

 (03 mag.), and, except for these, the fall of brightness 

 was slow but uniform until December 10, when the 

 magnitude was 5-67. The authors say that they were 

 disappointed not to detect any rapid changes of light. 

 Although the measures often extended over four or 

 five hours, there was only one night (June 10) when 

 a variation so large as o-io mag. could be estab- 

 lished, and the measures do not show any sudden and 

 erratic variations in the course of an hour or so. It 

 would, indeed, have been interesting if the large out- 

 burst between August 5 and 6 had happened in the 

 course of an evening's observations. Most of the 

 increases above mentioned have been recorded in other 

 series of observations. 



Mass and Momentum of Stellar Systems. — A 

 memoir of the College of Sciences of the Kyoto 

 Imperial University (vol. iii.. No. 7, August, 1918) is 

 useful, since it gives collected lists of binary and 

 multiple stellar systems, with the determined elements 

 of the orbits and the adopted parallax. From this 

 data the authors, Messrs. Shinjo and Watanabe, have 

 found that for all double and multiple systems the mass 

 is of the same order of magnitude, being in the mean 

 about one and a half times that of our solar system. 

 For spectroscopic binaries of the A type the mass is 

 found to be only slightly larger, but four spectroscopic 

 binary systems of the B type have in the mean a 

 mass' twenty times that of our system. A similar 

 research by Prof. Aitken recently showed that the 

 visual binarv systems were about twice as massive as 

 our sun, and suggested that stars of classes K and M 

 are less massive than those of classes A to G. The 

 authors of the memoir now before us computed 

 also the angular momenta of the systems, and found 

 that, on the whole, this is of the same order of magni- 

 tude for all visual systems, being more than a 

 hundred times that of' our solar system. That the 

 masses of the celestial bodies are, approximately, of 

 about the same order of magnitude has already been 



