August 22, 19 18] 



NATURE 



49 T 



different diameters and s^trengths the limit of per- 

 non was found in aU cases such that if there were 

 I ' absorption of light by the atmosphere a candle 

 would be visible at a distance of 27 kilometres. This 

 is equivalent to a staf of the eighth magnitude, and 

 it is probably the light of the sky which prevents stars 

 of higher magnitude than the sixth being visible. 



\ Engineering for August 9 has an illustrated article 

 { descriptive of an electrically welded barge, which has 

 been built at a yard on the south-east coast under 

 Government control. This barge is 120 ft. long and 

 16 ft, beam, and has a displacement of 275 tons. 

 The vessel, with full cargo, has been at sea during 

 exceptionally rough weather, and answered satisfac- 

 torily in every way to the test imposed. No rivets 

 were used in the construction, the whole of the struc- 

 ture being put together by electric welding. The 

 adoption of this system was a direct consequence of 

 experience in welding by means of the flux-coated 

 metal electrode process at the Admiralty dockyards. 

 There are seventy-one transverse frames in the barge, 

 with three bulkheads; plates of thicknesses i in. and 

 ^ in. were used for the shell plating. It is estimated 

 that future vessels of this size should be built with a 

 saving of 25 to 40 per cent, of time and about 10 per 

 cent, of material as compared with ordinary 

 riveted barges. The United States Shipping Board 

 is making arrangements for the building of a number 

 of 10,000-ton standard ships in which the use of rivets 

 will be reduced to about 2-5 per cent, of the normal 

 number. 



The problem of ascertaining the distribution and 

 magnitudes of the stresses in a revolving disc by 

 m.eans of mathematical formulae is tedious and com- 

 plicated. With the exception of the cases of discs of 

 constant thickness and constant strength, for which 

 definite integrals can be found, the analytical solution 

 involves highly complex equations, and the ultimate 

 result is doubtful. In the course of an article in 

 Engineering for August 9, Mr. H. Haerle describes 

 a method which can be applied to any sectional pro- 

 file and reduces the mathematical work to a minimum, 

 while at the same time results are obtained which 

 are suflficiently accurate for all practical purposes. 

 The general formulae are given by Dr. Stodola in 

 his book on steam turbines, and from these other 

 expressions are deduced for the sum and difference 

 of the principal stresses. Mr. Haerle has prepared a 

 chart showing the relation of these sums and differ- 

 ences with tangential velocities, and shows how the 

 chart may be applied to the solution of discs of 

 uniform thickness with and without a central hole, 

 discs of hyperbolic profile, and turbine discs having 

 the tapered sides usually employed in practice. An 

 example of an impeller disc for a turbo-compressor is 

 also worked out. Mr. Haerle's method gives remark- 

 able agreement with the mathematical method, and 

 certainly simplifies greatly an exceedingly complicated 

 problem. ' 



Mrs. M. T. Ellis contributes to the June issue 

 of the Biochemical Journal three interesting papers 

 on the plant sterols. In the first is recorded the 

 failure to isolate a typical phytosterol from the vegeta- 

 tive organs of the cabbage plant or from the faeces 

 of rabbits fed on a cabbage diet, although from, the 

 latter source a small quantity of a substance giving 

 the cholesterol colour reactions was separated. On 

 the other hand, cabbage-seeds contain a relatively 

 large amount of crystalline matter apparently similar 

 to the mixture of phytosterols present in rape-oil, 

 which is interesting in view of the fact that both rape 

 and cabbage belong to the genus Brassica. Grass- 

 NO. 2547, VOL. lOl] 



fruits also contain phytosterol, but a larger amount of 

 chortosterol. The second paper deals with the sterol 

 content of wheat, and it was found that the chief 

 phytosterol present both in the grain and in the embryo 

 is sitosterol. The bran contains a phytosterol, but pne 

 different from sitosterol. A method of estimating 

 phytosterol was devised based on the insolubility of 

 the compound of this substance with digitonin. The 

 quantity of phytosterol in the etiolated wheat-plant 

 is approximately the same as in the grain, but it is 

 higher in the adult plant. In the embryo the per- 

 centage of phytosterol is much higher than in the 

 plant, thus suggesting an essentiar function in ger- 

 mination and growth. In the third paper ("The 

 Occurrence of Phytosterol in some of the Lower 

 Plants ") it is shown that a mixture of ergosterol and 

 fongisterol, previously known to occur in fungi, is 

 present in Polyporus nigricans, and probably also in 

 P. beUdinus. From the alga Laminaria, the Musci 

 Sphagnum, and the fungi Agaricus ruhescens 

 and Lactarius subdulcis oils were obtained which gave 

 the cholesterol colour reactions. 



Messrs. BjxTERwoRrH and Co. (India), Ltd. (Cal- 

 cutta), have sent us a copy of their Medical Catalogue 

 for 1918. It is a very comprehensive list of works pub- 

 lished in Great Britain, India, and America on medi- 

 cine, surgery, dentistry, obstetrics, pharmacy, ophthal- 

 mology, and the allied sciences. As it is carefully 

 arranged according to subjects, and the prices are 

 given in Indian currency, it should be very useful to 

 medical men resident in India and the Far East, to 

 whom it will be sent free by the publishers upon 

 application. 



Messrs. T. C. and E. C. Jack, Ltd., announce two 

 forthcoming books by F. Martin Duncan, viz. 

 "Wonders of the Seashore" and "How Animals 

 Work." They also promise "Water in Nature," by 

 W. Coles Finch and Ellison Hawks. 



The Oxford University Press is about to begin the 

 publication of " Neurological Studies," from the Seale 

 Hayne Military Hospital, Newton Abbot. It will be 

 edited by Major A. F. Hurst, with assistance. 



OUR ASTRONOMICAL COLUMN. 



Wolf's Periodic Comet. — Mr. M. Kamensky has 

 further revised his orbit of this comet, applying per- 

 turbations by the earth, Mars, Jupiter, and Saturn. 

 His elements are given in Ast. Journ., No. 738:— 

 T = i9i8 Dec. 13-3909 G.M.T. 



o) =172° 54 41-83 ] 



^ = 206° 41' 31:71" I-19181 



/• = 25° 17' 31 -54"] 



0= 33° 58' 31-85" 

 ^ =522-42893" 



The Greenwich observations in July indicate the very 

 small correction +ooo46d. to the value of T. 



Ephemeris for Greenwich Midnight 



R.A. N. Decl. 



h. m. s. o / 



Sept. 3 ... 20 o 38 ... 22 20 

 7 .. 20 o 17 ... 21 13 

 II ... 20 o 36 ... 20 O 



15 ••• 20 I 36 ... 18 43 

 19 ... 20 3 17 ... 17 23 

 23 ... 20 5 39 ... 16 I 



27 ... 20 8 44 ... 14 37 

 Oct. I ... 20 12 31 ... 13 12 

 Values of log r, log A : September 3, 02726, 00274; 

 October i, 0-2415, 00242 respectively. 



The comet is nearest to the earth on September 20, 

 and the theoretical brightness is greatest on October 12. 



