544 



NATURE 



[April 6, 1905 



years ago, it has been found that bars which are con- 

 structed of copper alloys do not retain their originar length 

 with that degree of accuracy now demanded for scientific 

 purposes. The new copy (I. P.) is made of an alloy con- 

 taining 89-81 per cent, of platinum and loio per cent, of 

 iridium, such an alloy being little affected by changes of 

 temperature and not at all by oxidation ; as the alloy 

 admits of a high specular polish, the fine lines marking 

 the extremities of the yard can be traced directiv on the 

 bar without the intervention of gold plugs or pins as in 

 the older type. Instead of using the old solid i-inch 

 section, for the purpose of lightness the so-called 

 " Tresca " section has been adopted. The memorandum 

 gives full details of the verification of the length and a 

 description of the apparatus used, including the thermo- 

 meters by which temperature was measured and a new 

 microscopic " comparator " similar to that used at Paris 

 by the Comitd international des Poids et Mesures. This 

 instrument has been purchased by the Board of Trade and 

 mounted in a special chamber at Old Palace Yard, West- 

 minster. 



Vessels of fused quartz can now be obtained com- 

 mercially, and on account of the remarkable properties of 

 this substance, a wide field of research at high temperatures 

 would appear to be opened up by their use. In high 

 temperature gas thermometry, for example, where glass is 

 excluded on account of its comparatively low melting point, 

 and platinum on account of its permeability to hydrogen, 

 fused quartz promised to be an ideal envelope. Unfortunately, 

 Villard has found that fused quartz is also permeable to 

 hydrogen at high temperatures, well below its melting 

 point, and Jacquerod and Perrot have proved that helium 

 resembles hydrogen in this respect. In the current number 

 of the Coinl>tes rendtis (March 27) M. Berthelot shows that 

 the use of quartz vessels is still further limited, as both 

 oxygen and nitrogen can penetrate into hermetically sealed 

 quartz bulbs at 1300° C. Thus carbon, heated in sealed 

 vacuous quartz tubes for half an hour at 1300° C, gave 

 a mixture of nitrogen and carbon monoxide on cooling 

 the tube and extracting the gases. Experiments were 

 made on other substances, and all the facts pointed to the 

 conclusion that at a high temperature fused silica behaves 

 towards gases like an animal membrane, susceptible of 

 endosmosis and exosmosis, the phenomenon depending 

 partly on the thickness of the wall. It is clear, therefore, 

 that before this substance can be used with confidence in 

 high temperature work, a further study will have to be 

 made of its defects in this direction. 



The Comptcs rendus for March 27 contain an interest- 

 ing paper on the cryoscopic behaviour of hydrocyanic 

 acid, by M. Lespieau. According to the views of Nernst 

 and Thomson on the relation between the dielectric capacity 

 and the power of electrolytic dissociation, the fact that the 

 dielectric constant of prussic acid is higher than that of 

 water should give the acid a higher dissociating power. 

 M. Lespieau has accordingly carried out a series of ex- 

 periments on the lowering of the freezing point of this 

 substance by the addition of alcohol, chloroform, benzene, 

 water, trichloracetic acid, sulphuric acid, potassium iodide 

 and nitrate, and has found that for the first six substances 

 the cryoscopic constant is between 19 and 20, whilst for 

 the two latter it is approximately doqble. Hence the two 

 acids, which are strongly dissociated in water, are not 

 sensibly dissociated in prussic acid solutions of the same 

 strength, and this is in accord with the experiments of 

 Kahlenberg, who found that these solutions were bad con- 

 NO. 1849, VOL. 71] 



('uctors, these facts being in contradiction with Nernst's 

 .heory. On the other hand, the solutions of potassium 

 salts in hydrocyanic acid were found by Kahlenberg to be 

 better conductors than aqueous solutions of the same con- 

 centration, and this agrees with the cryoscopic results, 

 according to which the two salts are nearly completely 

 dissociated into their ions in prussic acid. 



Mr. \V. Woods Smyth will give a lecture on " The 

 Bible in the Light of Modern Science " at Stafford Rooms, 

 Tichborne Street, Edgware Road, to-morrow, .\pril 7, 



at s p.m. 



Messrs. Watts and Co. will shortly publish, for the 

 Rationalist Press Association, Prof. Haeckel's " Evolution 

 of Man," being a translation of the recently issued fifth 

 edition of " .Anthropogenic. " 



OVR ASTRONOMICAL COLUMN. 



Comet 1905 a (Gi.icobini). — A second telegram from 

 the Kiel Centralstelle announces that comet 1905 a was 

 observed by Prof. Aitken at Lick on March 27. The 

 position at March 27d. 7h. 57-101. (Lick M.T.) was 

 R.A. =5h. 4Sm. 55s., dec. = + 12° 35' 43". 



.Apparently, then, the northern declination is increasing, 

 and not decreasing as previously stated. .An error in the 

 key by which the code telegrams are translated substituted 

 declination for N.P.D., so that the daily movement in 

 declination should be read as plus 1° 15'. 



The following elements have been computed by Dr. E. 

 Stromgren from observations made on March 26, 28, and 

 30, and are given in Circular No. 76 of the Kiel Central- 

 stelle, together with a bi-daily ephemeris extending from 

 March 30 to April 23 : — 



Elements. 

 T = 1905 April 3-2093 (M.T. Btrlinl. 

 =0=357° 9' 49 I 

 48=156° 7' 94 19050 

 i - 41° 37'-4S ,1 

 log ry-= 0-05232 



Ephemeris 12/i. (M.T. Berlin). 



Brightness on March 26 =1-0. 



Photography of the Corona without a Total Eclipse. 

 — According to a note communicated to the French 

 Academy of Sciences, and in the opinion of M. J. Janssen, 

 .M. .A. ffansky has succeeded in photographing the corona 

 of the uneclipsed sun. The photographs were taken with 

 a 12-inch telescope in the exceptionally transparent atmo- 

 sphere which obtains at the observatory situated on the 

 summit of Mont Blanc. 



.After a number of preliminary experiments on the 

 selective absorption of screens dyed with various aniline 

 colours, .\I. Hansky obtained a combination which absorbed 

 all radiations more refrangible than 660 nfi, and, as the 

 red radiations of the corona are very intense and do not 

 suffer absorption or dispersion in passing through the 

 terrestrial atmosphere, ho used this screen in obtaining 

 twelve negatives. The individual screens were prepared 

 by soaking a fixed undeviloped Lumifere film in each of 

 the suitable dyes, and, beuveen each exposure, they were 

 re-arranged inter se so tli.nt no false effect due to any 

 particular disposition of the " grain " ntight affect the 

 resulting picture. The direct photospheric and chromo- 

 sphcric rays were prevented from reaching the plate by 



