49& 



NATURE 



[October 12, 191 1 



Rowland mounting for a concave grating. If a beam of 

 parallel light from a collimator falls on a transmission 

 grating, and is observed through a telescope after reflec- 

 tion, the spectrum is crossed by bands, which are due to 

 the interference of rays diffracted at the grating surface 

 and reflected from the back surface; rays transmitted 

 through the grating surface without diffraction, then re- 

 flected and diffracted on their return; and, lastly, rays 

 diffracted at the grating surface only. The authors develop 

 the method, and produce an interferometer which is easily 

 set up and possesses two degrees of sensitiveness, the 

 higher corresponding to about half a wave-length of light. 



An interesting sequel to their observations on optically 

 active substances containing no asymmetric carbon atom 

 (Nature, 1910, vol. lxxxvi., p. 93) is described by Profs. 

 Perkin and Pope in the August number of the Journal 

 of the Chemical Society. For this type of asymmetry 

 they propose the name " centroasymmetric," and their last 

 communication deals with the conversion of " centro- 

 asymmetric " compounds into derivatives containing asym- 

 metric carbon atoms, and vice versa. It is shown that, 

 although two isomeric derivatives are sometimes produced, 

 the optical activity of the compounds persists in all cases 

 in which the molecule remains asymmetric. The models 

 used by Prof. Pope in describing his observations to the 

 Chemical Section of the British Association at Portsmouth 

 are reproduced as photographs, the careful orientation 

 of which makes them even easier to understand than 

 the original solid figures. A point of considerable interest 

 is the description of a compound 



CI1, CH a .CH„ CI 



>c< cci.cn 



H CH„.C1I, X Br 



which owes its optical activity to an asymmetric atom 

 linked to the three univalent radicles H, CI, Br, the 

 asymmetric carbon atoms of all active compounds described 

 hitherto having been linked to at least two other carbon 

 atoms. 



A number of new uses of explosives in agriculture are 

 described by Mr. F. H. Gunsolus in the Journal of the 

 Franklin Institute for August. In the North-Western 

 Pacific States dynamite is largely used for clearing land of 

 tree-stumps ; but a more novel application is to drill holes 

 from 2 to 5 feet into the soil and to explode dynamite 

 cartridges in them, in order to break up and loosen the 

 subsoil. This process may be carried out on land where 

 orchards have already been planted, the quantity of 

 dynamite used varying from 25 to 100 lb. per acre. 

 Explosives are also being used very largely in the Western 

 States for digging ditches, especially in swampy clay 

 ground. Slanting holes are punched at intervals of about 

 2 feet along the line of the proposed ditch ; the middle hole 

 is loaded with two or three cartridges, the explosion of 

 which serves to detonate the charges in the other holes, 

 with the result that a mile or more of ditch may be blasted 

 simultaneously. The earth from the ditch is scattered 

 evenly over the adjoining land, and the presence of stumps, 

 trees, and underbrush interferes scarcely at all with the 

 success of the operation. 



A copy of the October issue of the catalogue of second- 

 hand instruments for sale or hire, by Mr. C. Baker, of 

 High Ilolborn, London, has been received. The list con- 

 tains particulars ol more than 1500 pieces of apparatus, 

 including a large selection of microscopes and astronomical 

 telescopes. Customers unable to call at the showrooms to 

 inspect pieces of apparatus can, on certain conditions, 

 hi m .hi approval for three days. 

 NO. 2189, VOL. 87] 



Tin; latest catalogue oi general chemical apparatus and 

 laboratory accessories issued by Messrs. A. Gallenkamp and 

 Co., Ltd., of Sun Street, Finsbury Square, London, L\C, 

 is likely to become a much consulted work of reference in 

 chemical laboratories. The profusely illustrated volume 

 runs to Soo pages, and provides full particulars, con- 

 veniently arranged, of all apparatus required for general 

 use in the laboratories of every grade of educational institu- 

 tion, and those of industrial works where apparatus for 

 research is employed. 



OUR ASTRONOMICAL COLUMN. 

 Beljawsky's Comet, 19111;. — From positions determined 

 on September 29 and October 1 and 3, Dr. Kobold has 

 calculated the following elements for the orbit of comet 

 191 ig, which has now become an object for evening 

 observations : — 



T =1911, October io"i96. 

 a =71° 39' 

 & = 88° 44' j-ign-o 

 i =96° 33 

 log q =9-4823 



From the ephemeris derived from these elements we give 

 the following : — 



Ephemeris 12ft. Berlin Midnight. 



* (irne) S (true) log r log . 



mag. 



Oct. 12 ... 13 376 ... +S 59-1 ... 9-4931 ... 0-0051 ... 2-4 

 ,, 14 ... 14 1 -o . +6 30-3 ... 9-5190 .. 0-0201 ... 26 



,, 16 ... 14 21-2 ... +3 43-9 ... 9-5545 •■• 0-0375 ... 2'9 

 „ 18 ... 14 38-5 ... +0 54-3 



,, 20 ... 14 53-2 ... -i 52-6 ... 9'<>355 ■■■ 0-0752 ... 3-4 



The calculated magnitude at perihelion was about 23, 

 but, owing to the rapid increase in distance, from both the 

 sun and the earth, it is decreasing rapidly, and with the 

 decreasing northerly declination the object is becoming a 

 difficult one to observe ; as the tail is approximately 

 vertical, however, it may be possible to observe it, low 

 down in the west, after the head has set, as was done in 

 the case of comet 1910a. 



Observations show that the tail, unlike that of Brooks's 

 comet (1911c), is of the broad parabolic type often 

 associated with great comets and small perihelion distances. 



According to a Times communication, Mr. Hinks 

 observed the comet between i6h. 30m. and 16I1. 45m. on 

 October 5, and estimated the magnitude of the nucleus as 

 3-5 ; only about 2° of the tail was visible. He also saw a 

 strong zodiacal light just before dawn. 



A tail 15° long was seen by Prof. Nijland, at Utrecln 

 October 1. 



Quenisset's Comet, 191 if. — The following is a further 

 extract from Dr. F.bell's ephemeris for comet ton/, which 

 is still observable throughout the earlier part of the 

 night : — 



Ephemeris \ih. M.T. Berlin. 



1, 1 1 a (nue) S(true) log r log A mag. 



h. m. , 



Oct. 12 ... 15 33-1 ... +38 19-3 ... 9-9903 ... 0-0252 ... 67 



.. 1 i ... 15 35-2 .. +35 119 



„ 16 ... 15 37-0 ... +32 14-4 ■■■ 9-9707 ...0-0409 6-7 



,, iS ... 15 38-5 ... +29 26-4 



,, 20 ... 15 398 26 47-5 ... 9-9519 ... 00754 ... 6-8 



All these positions lie near to a line joining p. and 8 

 Coronse, the comet's apparent path lying almost due south. 



Brooks's Comet, 1911c. — Brooks's comet passed the 

 sun on October 12, and became a morning comet; as 

 shown in the following abstract from Dr. Kobold 's 

 ephemeris, its apparent path now lies through Coma : — 

 Ephemeris 12ft. M.T. Berlin. 



ion a (true) {(true) log r log .i mag. 



Oct. 11 ... ij to-8 ... +30 2-5 ... 97970 ... 9-7^99 ■■■ 4'3 



„ 13 ... 13 2-6 ... +27 10-7 



,, 15 ... 12 55-4 ... +24 14-5 ... 9'75 8 3 ••• 9'Si78 •■• 2-8 



,, 17 ... 12 49-1 ... +21 16-1 



,, 19.. 12439 ... +18 15-5 ... 97241 ■•• 9S49S ». 2 ' 8 



,, 21 ... 12 397 ... +15 13-1 



