February 8, 1900] 



NATURE 



355 



Although but a short time has elapsed since the discovery 

 of the elements radium and polonium by M. and Mme. Curie, 

 a considerable amount of work has already been done upon the 

 properties of the rays emitted by these substances. M. Henri 

 Becquerel has already shown that there is a fundamental differ- 

 ence between the rays emitted by polonium and radium, in so 

 far as a portion of the radium rays are deviated by a magnet. 

 In the current number of the Comptes rendus is a further contri- 

 bution by M. Becquerel on this same subject, in which, after 

 showing that the deviation is the same in air and in vacuo, by 

 an ingenious arrangement it is shown that the rays given off by 

 different preparations are similar in nature, differing only in 

 intensity. The salts were placed in small leaden cups upon a 

 sensitised plate wrapped in black paper, and isolated from each 

 other by screens, no effect being produced upon the plate 

 until the magnetic field was excited. In a strong field the 

 radiation is bent down on to the plate, which, when developed, 

 showed that the deviations were equal, although of different 

 intensity. 



motion is at present following a north-westerly path through 

 Cetus. J 



Second New Algol Variable in Cycnus.— It is an- 

 nounced, in the Astronomische Nachrichten, No. 3614, that 

 Madam Ceraski, of the Moscow Observatory, has detected 

 another variable during the examination of plates taken at the 

 Observatory by M, Blajko. From the light variation observed, 

 it is considered to be of the Algol type. Its position is the 

 following : — 



R.A. 

 h. m. s. 

 18550 ... 19 40 597 



1900-0 ... 19 42 434 



The period is calculated to be 



6d. oh. 9 •4m. ; 



Decl. 



+ 32 21 6 



+ 32 27 34 



The exact value for the atomic weight of nitrogen, in spite of 

 its importance, is still liable to some uncertainty. The mean value 

 derived from the researches of Stas, Penny, Marignac, Pelouze 

 and Hibbs, by methods exclusively chemical, is 14034 

 (oxygen = 16) ; whilst the value calculated from the prac- 

 tically identical densities of Lord Rayleigh and Leduc is 

 14*006. The February number of \.\\g Journal oi the Chemical 

 Society contains further work on this subject by Mr. G. Dean. 

 Silver cyanide was obtained in a state of great purity, and the 

 ratio Ag : AgCN determined, from which the value 14 031 is 

 deduced for the atomic weight of nitrogen, a number practically 

 identical with the mean above quoted, I4"034. Further work 

 is clearly necessary to explain this considerable discrepancy, 

 nearly 02 per cent., between the results obtained by physical 

 and chemical methods. 



The additions to the Zoological Society's Gardens during the 

 past week include two Common Marmosets {Hapale jacchtis) 

 from Southeast Brazil, presented by Mrs. Nigel Cohen ; a 

 Black-eared Marmoset ^Hapale penicillata) from South-east 

 Brazil, presented by Mr. Hamilton Coffey ; a Rhesus Monkey 

 {Macacus rhesus) from India, presented by Dr. R. Cox ; a 

 Small Hill-Mynah {Gractila religiosa) from Southern India, 

 presented by Mr. W. Brindley ; two Dwarf Chameleons 

 (ChamaeleoH pu/nilus) iTom South Africa, presented by Mr. H. 

 Way ; a Lesser White-nosed Monkey ( Cercopithecus petau- 

 rista, i ) from West Africa, an American Bison (Bison anieri- 

 canus, <J ) from North America, two Great Anteaters {Myrnie- 

 cophagajubata, (J 9 ), a Blue-fronted Amazon {Chrysoiis aestiva) 

 from South America, deposited ; a Hog Deer [Cerims por- 

 cinus, <+ ) born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



CoMKTGiACOUiNlf 1900a).— A telegram, received February 3, 

 from the Centralstelle at Kiel, announces the observation of this 

 coniet by M. JavcUe, at the Nice Observatory, in the following 

 position : — 



R. A. 2h. 57 7m. ^ 1900 January 3id. 7h. 3m. 

 Decl. - 7° 55' / Nice Mean Time. 



A later telegram, received February 4, gives the following 

 position : — 



R.A. 2h. 49m. 51s. 1 1900 February 3d. 7h. 25-8m. 



Decl. -6" 40' 10" / Nice Mean Time. 



Daily motion in R.A = - 2 -65, 



,. M „ Decl. = - 25". 



The comet, when discovered, was about 2" north-ea.st of the 



4th magnitude star tj Eridani, and according to its observed 



NO. 1580, VOL. 61] 



an epoch of minimum being 



1899 December I5d. 23'3h. Greenwich Mean Time. 



The normal magnitude of the variable is 10, its value at the 

 minimum being about 12. 



A small chart of the neighbouring stars is given in the 

 paper to facilitate its recognition. The star makes almost an 

 equilateral triangle with the stars B.D. 32° "3559, and B.D. 

 32°-356o. 



The Compu iation of Occui.tations.— There is a consider- 

 able number of methods for calculating the times of occultations, 

 and until quite recently that of Bessel was the most generally 

 employed. In these computations, in order to obtain results 

 accurate to some seconds of time, the values resulting from the 

 first calculations were only taken as a first approximation and 

 used as a basis for a .second computation, which latter gave the 

 times with greater precision. In the year 1896 Dr. Carl 

 Stechert published a new method {Tafelii fiir die Voraus- 

 berecknung der Stetfibedeckttngen) which dealt directly with the 

 apparent and not the true time of conjunction, and at the same 

 time allowed of certain simplifications being made. Curiously 

 enough we have received from the Director of the Observatory 

 of Rio de Janeiro, Mr, L. Cruls, a description of a method 

 which results in an equation similar to that obtained by Dr. 

 Stechert, but obtained by a line of reasoning essentially 

 different. This method, which only involves one computation, 

 and is based on the exact knowledge of the instant of the 

 apparent conjunction of two stars, is fully described in the 

 publication referred to, the text being arranged in parallel 

 columns in the Spanish and French languages. The accuracy 

 of this method may be gauged from the results of ten com- 

 putations compared with the observed values. The mean error 

 of a single isolated observation was found to be + iis"5 while 

 that of the whole of the sixteen observations (including 

 immersions and emersions) was ± 3s. The method is 

 accompanied by numerous tables and diagrams for facilitating 

 the reductions of equations involved. 



Light Curve gi-- Ceraski's First Algol Variable.— In 

 the A stronotnical Journal, No. 475, Mr. J. A. Parkhurst gives the 

 results of forty-five observations of this variable during the period 

 1^99 Jwne 15 to September 12. Comparisons with four neigh- 

 bouring stars give the normal magnitude as 875, and the 

 minimum as 11 4, Forming the light curve from the observed 

 times and magnitudes, the epoch of an August minimum was 

 found to agree more closely with Prof. E. C. Pickering's value 

 (Harv. Coll. Obs. Circular, No. 44) than with that of Prof. . 

 Ceraski, so that the author supports Prof. Pickering's extension 

 of the period to 4d. I3h. 45m. 2s. 



Reduction ok Star Photographs.— Mr. A. R. Hinks, 

 who has recently undertaken the work of stellar photography 

 with the new photographic equatorial refractor at the Cambridge 

 Observatory, discusses, in the Astronomical /ournal. No. 475, 

 the method he proposes to adopt in the reduction of the plates. 

 The telescope is to be devoted to determinations of stellar 

 parallax, measures of star clusters, &c., and it is important for 

 the ultimate value of the work that the measures as published 

 should be comparable with others obtained elsewhere. Of the 

 many possible methods of reduction, the author considers it 

 most advisable to adopt a system based upon that devised for 

 the work of the Astrographic Catalogue by Prof. H. H. Turner 

 {Monthly Notices, R.A.S., 1894, vol. liv. p. 489). In thus 

 publishing the measures in the rectangular co-ordinates from the 

 plates themselves, there may be some doubt as to their being 

 comparable with older work published in the usual spherical 



