January 3, 19 18] 



NATURE 



35: 



film. The slope of the film at any point is found by 

 an optical method, and a number of diagrams of the 

 contour lines for various sections are given. The 

 diagrams thus obtained lead to a general method of 

 calculating the torsional strengths of rods of difficult 

 sections, which gives results much more accurate than 

 those at present in use. 



Messrs, P. L. Gainey and L. F. Metzler are the 

 authors of an interesting article entitled " Some Fac- 

 tors affecting Nitrate-Niirogen Accumulation in Soil" 

 in the Journal. of_AgricuUuraL Research (vol. xi., No. 2). 

 The soil employed in the work described was an 

 Oswego silt loam, and some preliminary experiments 

 led to the conclusion that the amount of nitrate pro- 

 duced is independent of the quantity of soil, of its depth 

 (provided the soil was left loose), of the ratio of the 

 exposed surface of the soil to its weight, and of the 

 shape and size of the containing vessel. These points 

 having been determined, experiments were made to 

 ascertain the effect of variations of the depth of 

 column, moisture content, and compactness of the soil 

 upon nitrate accumulation. From the results of these 

 experiments the following conclusions are drawn : First, 

 that the amount of nitrate increases with the compact- 

 ness of the soil, provided that the latter is not saturated 

 . with moisture. Secondly, the optimum moisture content 

 of the soil (with any degree of compactness tested) is 

 approximately two-thirds of the total amount of mois- 

 ture it will retain, and provided the moisture present 

 does not exceed this optimum, the aeration will be 

 adequate to a depth of one foot, however compact the 

 soil. Thirdly, the accumulation of nitrate increases 

 with increasing depth down to 2 ft. so long as the 

 moisture does not exceed two-thirds saturation. 

 Fourthly, that nitiate accumulates more rapidly in un- 

 •broken soil columns than in pulverised soil (in a 

 column of soil uncultivated for seven years aeration 

 was far greater than that required to maintain aerobic 

 conditions). The authors point out that such bene- 

 ficial effect as cultivating the soil may have upon its 

 biological activity cannot be attributed to increased 

 aeration, because the experimental data available for 

 normal field soils indicate that obligate aerobic condi- 

 tions almost invariably exist within the first foot of 

 surface. 



In the Atti dei Lmcei, vol. xxvi. (2), 6, Dr. Quirino 

 Majorana describes an exf>eriment performed with the 

 object of testing whether reflection from a mirror in 

 motion affects the velocity of light. For this purpose 

 a number of mirrors were arranged symmetrically round 

 a rapidly revolving- wheel, so that a pencil of light could 

 be reflected from a moving mirror, then from a fixed 

 mirror, then from another moving mirror, the process 

 being repeated any desired number of times so as to 

 increase the effect, and the mirrors having a com- 

 ponent velocity in the direction of the ray, and in a 

 M nse depending on that of the rotation. The change 

 in the wave-length produced by the rotation was ob- 

 ■,erved by a Michelson interferometer, the object 

 being to ascertain whether this change was 

 or was not the same as would take place if the 

 velocity of light remained constant. Although the 

 limits of error were considerable, it was found that 

 the results led to the conclusion that reflection from 

 a moving mirror does not change the velocity of light 

 relative to the surrounding medium. 



Messrs. C. Griffin and Co., Ltd., are about to 

 publish "Transmission Gears: Mechanical, Electric, 

 and Hydraulic, for Land and Marine Purposes," by e! 

 Butler, and new editions of " Coast Erosion and Pro- 



tection," by Prof. E. R. Matthews; "Mechanical En- 

 gineering for Beginners and Others," by R. S. 

 McLaren, and "Treatise on the Principles and Practice 

 of Harbour Engineering," by Dr. Brysson Cunning, 

 ham. Messrs. Crosby Lockwood and Son announce a 

 "Glossary of Aviation Terms" and "Aviation En- 

 gines," the former by Lieut. V. W. Pag6 and Lieut. 

 P. Montariol. and the latter by Lieut. Pag^. The 

 same firm will also issue a new edition of " Refrigera- 

 tion, Cold Storage, and Ice-making," incorporating the 

 fourth edition of " Refrigerating and Ice-making 

 Machinery," by A. J. Wallis-Tayler. "A Text-book 

 of Naval Aeronautics," by H. Woodhouse and others, 

 is promised by Messrs. T. Werner Laurie, Ltd. 



NO. 



2514, VOL. 100] 



OUR ASTRONOMICAL COLUMN. 



New Stars in Spiral Nebula. — A full account of 

 the discovery of a new star in the spiral nebula N.G.C. 

 4527 is given by Dr. H. D. Curtis in Lick Observatory 

 Bulletin, No. 300. Photographs from various sources 

 show that there was no trace of the star from early 

 in 1900 until March 20, 1915, when it appeared to be 

 of about 14th magnitude. On April 16 of the same 

 year it had fallen to 15th magnitude, and was not cer- 

 tainly recognised in later photographs. Two novae 

 were afterwards discovered in photographs of N.G.C. 

 4321, and of these also the history is fairly complete. 

 Including Ritchey's nova in N.G.C. 6946, six novae 

 have now been discovered in spiral nebulae, four of 

 them about 14th magnitude, and two brighter, one of 

 the latter being observed in the Great Andromeda 

 nebula in 1885. Dr Curtis considers that the appear- 

 ance of these novae strongly supports the view that 

 the spiral nebulae are "island universes." The 

 average maximum brightness of novae which 

 have appeared in our own galaxy is about 

 magnitude 5, and if the galactic and spiral 

 novae have the same absolute brightness, the difference 

 of about^ 10 magnitudes indicates that the spiral nebulae 

 in question are of the order of 100 times as far away 

 as the galactic novae, which are themselves known to 

 have been very remote. Five additional novae in spirals 

 are included in a list given in Popular Astronomy, 

 vol. XXV., p. 632. 



"Companion to the Observatory for 1918." — The 

 issue of this publication for 19 18 closely resembles 

 those of previous years. In addition to a convenient 

 series of tables relating to the sun, moon, and planets, 

 and the satellites of Jupiter and Saturn, it includes an 

 extensive catalogue of meteor radiants, and tables 

 giving the times of minima or maxima of a large 

 number of variable stars. The list of double stars has 

 been improved by the addition of the periods of revo- 

 lution, so far as they have been determined, and it now 

 includes practically all the visual binaries of known 

 period. There is arlso a useful table of astronomical 

 constants. 



Hyderabad Observatory Report. — The report of 

 the director of the Nizamiah Observatory, Hyderabad, 

 for the year ending October 5, 19 17, is chiefly note- 

 worthy as indicating that great progress has been made 

 with the astrographic work. The catalogue for zone 

 - 17° has been finally passed for press, and the greater 

 part of that for -18° is also in the hands of the 

 printers. For zone -19° 131 plates, containing 46,186 

 stars, were taken, measured, and reduced during the 

 year, and fifty-three plates for zone -20° were also 

 taken and partially measured. Mr. Pocock is to be 

 congratulated on having so quickly brought this insti- 

 tution to a high state of efficiency. 



