December io, 1908] 



NATURE 



109 



can be tested. There are also devices by means of which 

 the unidirectional character can be brought about, but 

 these devices usually impair the performance of the tube. 

 We have had the opportunity of examining an arrange- 

 ment recently brought out by Messrs. F. R. Butt and Co., 

 of II Denmark Street, W.C. The usual primary of the 

 induction coil is surrounded by a subsidiary coil consist- 

 ing of a single layer. This second coil can be short- 

 circuited at any time, and it is so connected with a re- 

 volving break that it is short-circuited just prior to the 

 make of the primary. The induced E.M.F. at the 

 secondary terminals is thereby so far diminished that no 

 discharge occurs there at the make. The subsidiary coil 

 is immediately afterwards interrupted by the revolving 

 break (and for greatest efficiency this interruption must 

 occur when the current in the primary coil has a stationary 

 value) ; the discharge at break of the primary circuit 

 then takes place without being in any way reduced by 

 the presence of the subsidiary coil. The result is a uni- 

 directional current as perfect as could be desired. There 

 are other details of the coils turned out by this firm 

 which are of interest. In particular, the iron core, con- 

 sisting of iron wires, is laid with these wires arranged 

 in groups, which are insulated from one another with 

 the object of thoroughly preventing the formation of 

 Foucault-current circuits in the iron. 



.A SUPPLEMENTARY list of new apparatus for physical 

 demonstrations, just issued by Messrs. Newton and Co., 

 contains particulars of the nature and use of a number 

 of important instruments. By arrangement with Mr. W. 

 Duddell, F.R.S., Messrs. Newton are enabled to supply 

 the complete apparatus for his well-known experiments 

 with musical arcs. A universal optical bench and projec- 

 tion apparatus, designed by Mr. F. J. Cheshire, provide 

 a means of demonstrating many important facts as to 

 light and colour bv projection. The same apparatus, with 

 accessories, can be used to illustrate the optical properties 

 of the human eye, and the principles of the telescope, 

 microscope, and other optical instruments. Dr. R. S. 

 Clay's apparatus for the production of waves and ripples in 

 water and their projection upon a screen provides a particu- 

 larly instructive means of illustrating interference effects. 

 Lecture-table apparatus to demonstrate the properties of 

 selenium and their application in the transmission of 

 pictures by telegraphy is also described, together with 

 other devices of interest to teachers and students of physics. 

 The list should be seen by all who are contemplating the 

 provision of new apparatus necessary for modern physical 

 demonstration. 



OUR ASTRONOMICAL COLUMN. 



The Spectrum of Comet Morehouse, igoSc. — In No. 21 

 of the Comptes rcndiis (November 23, p. 951) MM. 

 Deslandres and Bosler publish some very interesting results 

 derived from spectrograms of comet 1908c, taken with a 

 slit spectrograph of 012 m. (47 inches) focal length, and 

 a ratio of aperture to focal length of about i : 3. 



On spectrograms obtained previously with a prismatic 

 camera, MM. Deslandres and Bernard found that certain 

 lines of unknown origin in the spectrum of this comet, as, 

 also, in that of comet Daniel photographed last year, were 

 double, and it was partly to determine the reality and 

 nature of this doubling that the slit spectrograph was 

 employed. 



Two spectra were obtained, and they show that double 

 lines really do exist at the approximate mean wave-lengths 

 47000, 456-10, 453-10, 426-7, and 401-3. Moreover, the 

 intervals between the components vary, appro.ximately, with 

 the wave-length, so that the ratio AX/X is practically 

 constant. 



NO. 2041, VOL. 79] 



.Another remarkable feature, noted in the case of those 

 radiations produced by the tail, is that the Imes show 

 different inclinations to the length of the spectrum and ,t 

 is suggested that this may be due to the fact that the 

 particles of matter emitting the respective radiations were 

 being acted on differentially bv the solar repulsion ; it tnis 

 is the true explanation of the phenomenon, we have an 

 experimental proof of the truth of Bredichin's theory. 



In the longest lines, extending well into the tail, there 

 is also a marked inflexion at some distance from the head, 

 and the authors suggest that this phenomenon may be due 

 to rotation of the tail. . .^ 



Previous researches with the prismatic camera gave MM- 

 Deslandres and Bernard no indications of polarisation in 

 the^ components of these doublets ; it therefore seems prob- 

 able that the doubling is not a Zeeman effect, brom tne 

 fact that the intervals separating the components appear 

 to bear a constant ratio to the wave-length, ,t would seem 

 rather to be a Doppler effect, but the researches J^^^^JJl 

 carried much further ere any conclusion can be dehmtelv 

 accepted. 



The Changes in the Tail of Comet Morehouse.- 

 From No. 12 of the Gazette astrononnque November 30, 

 p 93) we learn that the photographs of Morehouse s comet 

 faken at the Juvisv Observatory, confirm the peculiar 

 phenomena of the tail observed at G-eenw.ch Stonyhurst 

 and other observatories. Not only do they show the ebb 

 and flow of activity, probably caused by the comet 

 encountering masses of meteoritic matter of different densi- 

 ties but thev also afford proof that the conspicuous 

 agglomerations in the tail suffered an acceleration m 

 vdocity as they receded further and further from the head. 



Determination of Longitude by Wireless Telegraphy. 

 -TulVLptes rendus for November 2 (p. 8'9) -;/-';^^ 

 a report, bv M. Bouquet de la Grye on behalf of the 

 wirel^s teiegraphv committee of the Academie des 

 Sciences, dealing with the subject of the determination of 



longitude at sea by the aid of ^^■'r<^'<^'%'"'''='']r-„;^-,<,ators 

 After reviewing the immense importance to navigators 

 of* this question, and the various methods by whicfi longi- 

 tudes have hitherto been determined, the -P-'f cusses 

 the possibilitv of sending signals, at P;-^-?^^""^ ^^'^Xi 

 from'^he summit of the Eiffel Tower. .^^ .''.'''"'^^^f.^^^l 

 such signals could be sent, say, at midnight ^hen there 

 would be least interference, and that ships in am part ot 

 he Atlantic, for example, could thereby ;77« . ^^ 

 correct time necessary for the determination °f '" S^^"f j 

 A recommendation that the necessary experimental 

 apparatus be erected on the Eiffel Tower •''^J^^" ^ 

 possible was elicited from 'V, '^"'T 1 t%h; Ministers 

 endorsed bv the committee, and forwarded to the Ministers 



of War and .M.iri:.. 



Spectroscopic BiNARiES.-The November number of the 

 Astrobhvsical Journal (vol. xxviii., No. 4) contains t\vo 

 papers bv Mr. Plaskett, of the Dominion Observator>, 

 Ottawa, dealing respectively \vith the orbits of the spectro- 

 scopic binaries 4i and t Orionis. „ 1 „^ 



For the former, the results show an abnormally large 

 range of velocity, about 288 km., and a period of 2-525S8 

 days; the apparent length of the semi-major axis of the 

 orbit is 4.QQs.ioo km. _ , j i. 



The application of a least-squares solution to the data 

 o-iven previouslv for the orbit of i Orionis has amended 

 The orbit to some extent. The final elements give the 

 ellipticitv as 0-7543+0.0046, the period as 29-136 days, and 

 the apparent length of the semi-major axis as 

 28,907,000 km. 



A Recent Observation of Nova Cygni.— Froiii a plate 

 exposed for two hours, Dr. Karl Bohlin estimates that Nova 

 Cvgni (No. 2), 1876, was of the fourteenth magnitude on 

 October 22. From January 8, 1877, to March 24. 1882, the 

 magnitude of this object sank from 67 to 140, and recent 

 measures have given the following magnitudes :— Burn- 

 ham, 1891-6, 13-5; Barnard, 1901-9, iS'^; Bohlin, 1908-8, 

 13-5. On the Dunecht scale of magnitudes Barnard s and 

 Bohlin's results are between 150 and 14-3, and 14-0 re- 

 spectively (Asfronomische Nachrichtcii, No. 42S6, p. 22b. 

 November 28). 



