24 



NATURE 



[January 5, 1922 



of the effects observed in the ternary system is 

 impossible. It follows, therefore, that many of the 

 data obtained are as yet purely empirical. 



We learn from the Times of December 27 that 

 Major Klein is at work on a three-colour printing 

 process in which the chief innovation is in the taking 

 of the colour records. Instead of the usual light- 

 filters attached to the camera he illuminates the object 

 with light of the desired colour obtained by the well- 

 known method of cutting off with opaque screens the 

 light not wanted in a spectrum produced by suitable 

 spectroscopic apparatus. It seems that he proposes 

 to try the effect of reducing the width of the utilised 

 portions of the spectrum so as to get a nearer ap- 

 proach to monochromatic light, and also the division 

 of the Spectrum into more than three parts for four 

 or five, etc., colour processes. 



In the December issue of the Journal of the Society 

 of Chemical Industry Dr. G. C ' Clayton contributes 

 an interesting summary of the effect of the war on 

 the heavy chemical industrv. The Leblanc soda in- 



dustry is stated to be obsolete, and many of the by- 

 products formerly obtained by it have now to be pre- 

 pared by other methods. One of the main products, 

 caustic soda, is now made either from ammonia-soda 

 carbonate or by electrolysis. The two chief electro- 

 lytic processes operated in this country are the mer- 

 cury process, by the Castner-Kellner Co., and the 

 Gibbs diaphragm process, by the United Alkali Co. 

 In the manufacture of chlorine the Weldon and 

 Deacon processes have been displaced by the elec- 

 trolytic methods. Electrolytic chlorine is produced 

 by the Castner-Kellner, Gibbs, and Hargreaves cells, 

 and is often liquefied. Chlorates are now made only 

 by electrolysis of chlorides. 



M. GoMBERG and C. C. Buchler describe in the 

 j August number of the Journal of the American 

 ! Chemical Society the preparation of benzyl ethers of 

 carbohydrates. Glucose, sucrose, dextrin, starch, and 

 cellulose are readily benzylated, and some of the pro- 

 ducts may be of technical importance from their col- 

 loidal and plastic characters. 



Our Astronomical Column. 



The Einstein Tower. — The Observatory for 

 December contains an illustrated article on this tower, 

 which has just been erected in the grounds of the 

 Potsdam Astrophysical Observatory. It contains a 

 vertical telescope of 50 cm. aperture and 14^ metres 

 aperture, fed by a coelostat. There are two spectro- 

 graphs, one with a plane-grating of 12^ cm. aperture, 

 the other with two large prisms giving a dispersion of 

 two angstroms to i mm. The instrument will be 

 chiefly employed to investigate the presence or 

 absence of the Einstein shift, but it is available for 

 general astrophysical work. It is in charge of Dr. 

 E. Freundlich, under the general control of Prof. 

 Einstein, who has now an appointment at Potsdam. 

 Dr. Freundlich hopes to observe next year's eclipse 

 from Christmas Island, with A. Kohlschiitter and 

 Dr. VoOte. 



Changes in the Crab Nebula. — One of the verv 

 useful researches to which the great American tele- 

 scopes have been applied is the study of changes in the 

 nebulae, by comparison of photographs taken at in- 

 tervals of a few years. The changes have been in 

 many cases unexpectedly large, and imply either rela- 

 tive nearness to the solar system or very high internal 

 velocities. 



Mr. Lampland had already reported some changes 

 in the Crab Nebula deduced from seventeen photo- 

 graphs- taken with the Lowell 40-inch reflector during 

 a period of eight years. Mr. John C. Duncan gives in 

 Proc. Nat. Acad. Sci., June, ,1921, the results of a 

 comparison of two photographs taken with the 60-inch 

 reflector at Mount Wilson at an interval of eleven and 

 a half years (iqog and 192 1). 



Twelve condensations were selected near the outer 

 contour of the nebula, at tolerably equal intervals. 

 Thirteen comparison stars were chosen, one near the 

 centre of the nebula, the others fairly near the selected 

 condensations. The results may be summed up thus : 

 (i) the motions of the condensations are on the 

 average quite three times as great as those of the 

 stars ; (2) while the star-motions are at random as 



NO. 2723, VOL. 109] 



regards direction, those of the condensations are 

 systematically outward from the centre, being greatest 

 at the ends of the long axis of the nebula, where they 

 amount to 2" in eleven and a half years, implying a 

 linear speed of 25 km. /sec. at an assumed distance of 

 one hundred light-years. There is some (not very cer- 

 tain) evidence of a counter-clockwise rotation of the 

 nebula. The mean motion of all the nebular conden- 

 sations in eleven and a half years is +o-io" in R.A., 

 + 0-435" in Decl., referred to the mean of the stars. 



The AsTROGRAPHic Catalogue. — The publication of 

 this great work was considerably in arrear even before 

 the war, which, naturally, did not tend to improve the 

 situation. It is satisfactory to note that volumes are 

 now appearing in rapid succession. 



Mr. H. B. Curlewis, director of Perth Observatory, 

 West Australia, has catalogued the whole of zone 



— 35°, the numbers of stars in each quadrant being 

 6879, 24,753, 22,139, 19,277. The paucity in the first 

 quadrant is explained by its proximity to the South 

 Galactic Pole. The magnitudes are given by letters, 

 A denoting 85, B 90, and so on ; the scale used is 

 that of Chapman and Melotte, and differs from that 

 used in earlier Perth volumes. 



Mr. T. P. Bhaskaran has produced vol. 4 of the 

 Hyderabad section, which catalogues the whole of zone 



— 20°, the number of stars being 79,590. This volume 

 completes the zone originally allotted to Hyderabad, 

 about half the plates of which had been taken and 

 measured before the death of Mr. Pocock in 1918. 

 The work has been completed on the lines laid down 

 by him. Standard co-ordinates of all stars contained 

 in the Algiers Astr. Gesells. Catalogue are given at the 

 end of the volume. 



Senor Leon Herrero, director of San Fernando 

 Observatory, has produced the first half of the cata- 

 logue for zone —3° (R.A. oh. to i2h.). It contains 

 58,387 stars, and diff'ers from most of the catalogues 

 in containing X„, Y„ co-ordinates for all stars, in addi- 

 tion to the measured a;, y. 



