June 13, 1895] 



NATURE 



!.■>:) 



sulphide will serve to illustrate the method followed. Twenty 

 grams of bismuth were melted in a covered crucible, and two 

 grams of silver sulphide were added. By solution of the slowly 

 cooled product in nitric acid of specific gravity ii, there re- 

 mained small dark crystals intermixed with silver -white crystals. 

 The latter consisted of a bismuth-silver alloy, and, in time, dis- 

 si lived in the acid. On drying, the remaining dark crystals were 

 ri)un<l to possess a steel-blue lustra. They formed pretty groups 

 'if oclahcdra (figure given in the paper) attached in rows. 

 .Vnalyses proved their composition to be well represented by the 

 formula, .\gBiS._, or .-^g.^S -i- BioS^. 



In the current number of the Comptesr^itdiis^ M. Cleve gives the 

 results of a determination of the density of the new gas helium by 

 .M. I-anglet. The gas, extracted from cleveite, was freed from 

 hydrogen by passage over red-hot copper oxide, and from 

 nitrogen by metallic magnesium. It contained no argon. The 

 density was found to be notably less than the number given by 

 I'rof. Ramsay, being OT39 (air = i) or 2-02 (hydrogen = I). 

 The determination of the specific heat of the gas has Ik en taken 

 in hantl by the same investigators ; their results will be awaited 

 with much interest. 



The additions to the Zoological Society's Oardens during the 

 past week include two Rhesus .Monkeys (Maiams rhesus, i5 9 ), 

 from India, presented, respectively, by Sir Henry W. Peek, 

 and .\Ir. R. Kdmeades ; a Patas Monkey (Cenopitheciis 

 (ruber, <}), {torn West Africa, presented by Mr. C. H. Armit- 

 age ; a Campbell's Monkey (Cereopitliecus campbelli, i), from 

 West Africa, presented by Miss L. Panther ; a Herring Gull 

 (Larus argentalus], Briti.sh, presented by Mr. J. T. Oorvin ; 



three Ocellated Skinks (Sepsocel/atus), a. Skink (ChaUides 



.«•/>()/</«), a Defenceless Lizard (Agama i>iermis),\.v,o Diademed 



Snakes (Za/uenis diadema), two .Snakes (Calopeltis 



nioileiisis), four Egj'ptian Eryx (Eryx jaculus), two Cerastes 

 \ilK'rs ( Vipera cerastes), two Egyptian Cobras (Naia haje), from 

 Lower Egypt, presented by Dr. John Anderson, K. R. S. : a 

 White-crowned Monkey ( C<moce'i5«^ lelhtops), a White-necked 

 .Stork (Dissura episcopus), from West Africa ; two White 

 Pelicans ( Pelecanusonocrolaliis), from North .\frica ; aBarraband's 

 Parrakeet (Polylelis barrabandi), from New South Wales ; three 



Hamadryads (Ophiophagus elaps), from India : fifty Tree 



Krogs(/i5'/a ), from America, deposited; a Red Deer ( Cfrc'/« 



elaphus), an Argus Pheasant (Jrgus giganteus), three Ruddy- 

 headed Geese {Rernicla rubidictps), bred in the Gardens. 



OUR ASTRONOMICAL COLUMX. 



CoMKT 1892 \. (Bar.nakI)).— The orbit of this comet, which 

 had been discussed by Mr. J. G. Porter (Astroiioiiikal Journal, 

 No. 310), has recently been made the subject of a further invesli- 

 galiim by M. J. Coniel : but the elements, resting as they do 

 on a very few observations, still remain uncertain to a consider- 

 able extent. The comet was discovered, photographically, on 

 Oclolier 12, 1892, and regular observatitms do not extend beyond 

 November 22, 1892, about six weeks only from the date of dis- 

 covery ; l)ut an isolated observation made at Nice on December 

 8, not taken into the discussion by Mr. Porter, induced M. J. 

 Coniel (o reopen the inquiry, with the hope of making a better 

 determinalioii of the period. Mr. Porter's orbit represented 

 this observation within the errors - 005s. and - I2'9, in R..A. 

 and Declination respectively ; and considering the difficulty of 

 the ()l)serv.ilion, such a discrepancy is not more than might be 

 anticiiiated, and consequently does not suggest the possibility of 

 decided improvement. The feature of the more recent discussion 

 is ti« show that the observations can be equally well .satisfied 

 with elements in which the mean daily motion is altered by some 

 26". This is not quite the twentieth part of the whole motion, 

 therefore the jjeriod is uncertain to its twentieth part, or about 

 0-3 of a year. 



.M. Coniel judges that the uncertainty in the mean motion 

 may extend to 25' on either side of his result, and that the period 



^'O- ^17)1 ^ VOL. 52] 



may lie between 6-23 and 6-84 years. The consequence of this 

 uncertainty is that the search for the comet at future returns must 

 be greatly extended. In I S99, the sweeping ephemeris must be 

 based on a mean motion corresponding to 6 •65-6 '84 years. In 

 1905, the comet may be visible if the period lies between 6-34- 

 6-55 years : while in 191 1, and even 1912, the return may be 

 expected with still other and possible values of the mean motion. 

 No near approach to Jiqjiter will take place during this intenal, 

 but the situation of the orbit is such that the comet can approach 

 both Jupiter and .Mars. Confining attention to the most probable 

 period (652 years), the comet approaches the orbit of Jupiter 

 within ooyrv, in Hel. Long. 207°, and that of Mars within 

 OOI2R, in Hel. Long. 28^ This interest in the comet's path 

 is still further increased by the speculation, due to M. Schulhof, 

 that this comet formed originally a part of Wolfs comet, from 

 which it possibly se|>arated in 181 5. 



Me.^slrement ok Radi.\i, Velocities. — The methods at 

 present employed for the measurement of the movements of the 

 heavenly bodies towards or away from the earth usually involve 

 the use of a comparison spectrum, whether the observations be 

 made by eye or by photography. In special cases, however, 

 other methods are employed, as, for example, the use of telluric 

 lines by Duner in the measurement of the suns rotation. It h-is 

 not, however, yet been considered practicable to utilise the 

 objective prism for the work, on account of the difficulty of 

 obtaining reference spectra. -\ new method, which has the 

 great advantage of being applicable to spectra photographed 

 with or without slits, has recently been suggested by .M. 

 Orbinsky, of Odessa. (As/r. Xac/i. 3289. ) The principle of the 

 method is based on the fact that the displacements of lines are 

 different at different wave-lengths, so that the distance be- 

 tsveen two lines in a spectrum depends upon the velocity 

 of the source of light ; the higher the velocity, the greater or less 

 will be the distance between any two lines in the spectrum, 

 according as the source of light is approaching or receding, and 

 providing the dispersion be sufficient, it may be possible to 

 measure the velocities l)y this means. Obviously the measure- 

 ments are much more delicate than the direct measures of the 

 displacements. In practice it is proposed to employ reference 

 stars, the velocities of which have been determined in the 

 ordinary way by photographic comparison spectra of hydrogen or 

 iron, fine of these Iwing photographed on the same plate as 

 the star under investigation, the results will give the velocity re- 

 latively to the comparison star, and hence the absolute velocity. 

 The instruments emiili>yeil should give the greatest jx)ssible 

 range of wave-lengths, and it will be specially advantageous to 

 obtain as great a difference of dispersion as possible between the 

 extreme ends of the spectrum. It is shown by actual figxires 

 that the measurements are quite practicable, both in the case of 

 the PoLsdam spectrograph and in the objective prism employed 

 at Harvard College. It is in the case of the latter class of 

 instruments that the method seems most likely to be of practical 

 value. 



Two Remarkable Bi.narv Stars. — Apart from the binary 

 stars which can only be recognised as such by the aid of the 

 spectroscope, the two binary stars of shortest periods at pre- 

 sent known are k Pegasi and 5 Equulei. The orbits of these 

 have been redetermined by Dr. See, using all available obser- 

 vations, many of which are due to the industry' of Profs. 

 Burnham and Barnard. The elements deduced are as follows 

 {Aslr. Nai/t. 3285, 3290) :— 



K PcK.irii. 6 Equulei. 



P ... 11-42 years ... 11-45 years 



T ... 1S96-03 1892-8 



t ... 0-49 0-14 



a ... o'-42i6 o"-452 



I ... Si'-2 79''05 



a ... n6°-2S 22°-2 



A ... 89'-2 o°-o 



n ... -3'°'5236 ••• -3>°'44i 



Prof. Burnham has repeatedly called attention to the impor;- 

 ance of systematic observations of rapid binaries with large 

 telescopes, so that ive should in a few years get good orbits, 

 which in the case of most binaries would require the observations 

 of centuries. 



It will l)e seen that there is still a great gap between the 

 telescopic and spectroscopic binaries, but it is quite possible that 

 as the powers ot both instruments are increased the gap may l>e 

 gradually shortened from both sides. 



