454 



NATURE 



\Apru% 1874 



M. Gosselet furnishes a detailed account of the southern band of 

 Devonian limestones in the district Entre Sambre-et-Meuse ; and 

 M. Selys de Longchamps makes some additions to a synopsis of 

 the Cordulina. — A programme of five questions for medal compe- 

 tition is announced, the suljjects being briefly these : distui'bing 

 causes in determinaiion of the electromotive force and inferior 

 resistance of a battery element ; relations of heat to the phe- 

 nomena (especially periodic) of vegetation ; embryonal develop- 

 ment of Tunicata ; composition and mutual relations of albumi- 

 noid substances ; coal system of the Liege valley. 



Arclnves des Sciences Physiques et Nalnnlles, Feb. 15, 1874. — 

 In this number M. Dufour gives a detailed account of his re- 

 searches on the variation of temperature which accompanies dif- 

 fusion of gases through a porous partition. After describing the 

 apparatus (in which a porous vessel, with thermometer and other 

 tubes inserted in its gutta-percha stopper, was enclosed in a 

 cylindrical glass vessel, and this, enveloped in loose cotton, in a 

 larger earthen vessel), the author studies first the influence of the 

 dry or humid state of gases coming into contact with the porous 

 wall, without diffusion ; next, variation of temperature where 

 there is no change of pressure ; and third, variation where there 

 is such change. With constant pressure, there is fall of tempe- 

 rature on the side where the denser gas is ; and rise on the other 

 side. Each current seems to have a healing effect where it 

 enters the porous wall and a cooling one wht;re it issues. With 

 change of pressure, where this rises wiihin the vessel, through 

 endosmose of a lighter gas, the temperature slightly increases, 

 sinking again as the pressure tends to equilibrium. Where 

 exosmose of a lighter gis causes diminution of pressure in the 

 vessel, the reverse occurs. — From observations of the partial solar 

 eclipse of May 26 last, at three Italian stations, D'Aoste, Monca- 

 lieri, and Florence, Prof. Denzi finds no sensible influence on 

 the declination needle, either as regards its regular diurnal move- 

 ment, or the absolute value of its displacement. He is confirmed 

 in the conclusion, previously formed (on data of former eclipses), 

 that no connection has hitherto been demonstrated between the 

 two orders of cosmic facts, eclipses and phenomena of terrestrial 

 magnetism. — M. Charles Lory communicatee a note on some 

 facts of structure in the central chains of the Alps. — The Bulldin 

 Scientijiqne gives, as usual, a valuable scries of notes on recent 

 progress in Physics, Geology, Zoology, and other branches. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, March 26. — On the Motions of some of t'.u 

 Nebulas towards or from the Earth, by William Huggins, 

 D.C.L.,LL.D.,F.R.S. 



The observations on the motions of some of the stars towards and 

 from the earth, which I had the honour to present to the Royal 

 Society in 1S72, appeared to .show, from the position in the 

 heavens of the approaching and receding stars, as well as from 

 the relative velociiies of their approach and recession, that the 

 sun's motion in space could not be regarded as the sole cause of 

 these motions. " There can be little doubt but that in the ob- 

 served stellar movements we have to do with two other inde- 

 pendent motions — namely, a movement common to certain 

 groups of stars and also a motion peculiar to each star." * 



It then presented itself to me as a matter of some importance 

 to endeavour to extend this inquiry to the nebulae, as it seemed 

 possible that some light might be thrown on the cosmical rela- 

 tions of the gaseous nebulae to the .stars and to our stellar 

 system by observations of their motions of recession and 

 approach. 



Since the date of the paper to which I have referred, I have 

 availed myself of the nigtits sufficiently fine (unusually few even 

 for our unfavourab'e climate) to make observations on this 

 point. The inquiry was found to be one of great difficulty, from 

 the faintness ol the objects and the very minute alteration in 

 position in tfie spectrum which had to be observed. 



Al first the inquiry appeared hopeless, from the circumstance 

 that the briglitest line in ttie nebular spectrum is not sufficiently 

 coincident in character and position with the brightest line in 

 the spectrum ol nitrogen to permit this line to f)e used as a 

 fiducial line of comparison. The line in the spectrum of the 

 nebuljB is narrow and defined, while the line of nitrogen is 

 double, and each component is nebulous and broader than the 



* Proceedings of the Royal Society, vol. xx. p. 392. 



line of the nebulae. The nebular line is apparently coincident 

 with the middle of the less refrangible line of the double line of 

 nitrogen. * 



The third and fourth lines of the nebular spectrum are un- 

 doubtedly those of hydrogen, but their great faintness makes it 

 impossible to use them as lines of comparison under the neces- 

 sary conditions of great dispersive power, except in the case of 

 the brightest nebulse. 



The second line, as I showed in the paper to which I have 

 referred, is sensibly coincident with an iron line, wave-length. 

 495 7 ; l'"t this line is inconveniently faint, except in the 

 brightest nebulx. 



In the course of some other experiments my attention was 

 directed to a line in the spectrum of lead which fdls upon the 

 less refrangible of the components of the double line of nitrogen. 

 This line appeared to meet the requirements of the case, as it is 

 narrow, of a width corresponding to the slit, defined at both edges, 

 and in the position in the spectrum of the brightest of the lines 

 of the nebuhe. 



In December 1S72 I compared this line directly with the first 

 line in the spectrum of the Great Nebulae in Orion. I was de- 

 lighted to find this line sufficiently coincident in position to serve 

 as a fiducial line of comparison. 



I am not prepared to say that the coincidence is perfect ; on 

 the contrary, I believe that if greater prism power could be 

 brought to bear upon the nebulae, the line in the lead spectrum 

 would be found to be in a small degree more refrangible than the 

 line in the nebulae. 



The spectroscope employed in these observations contains two 

 compound prisms, each giving a dispersion of 9° 6' from A to 

 H. A magnifying-power of 16 diameters was used. 



In the simulianeous obsei-vation of the two lines it was found 

 that if the lead line was made rather less bright than the nebular 

 line, the small excess of apparent bread h of this latter line, 

 from its greatei brightness, appeared to overlap the lead line to 

 a very small amount on its less refrangible side, so that the more 

 refrangible side of the two lines appeared to be in a straight line 

 across the spectrum. This line could be therefore conveniently 

 employed as a fiducial line in the observations I had in view. 



In my own map of the spectrum of le d this line is not given. 

 In Thalen's map (1S6S) the line is represented by a short line to 

 show that, under the conditions of spark under which Thalen 

 observed, this line was enitted by those portions only of the 

 vapour of lead which are close to the electrodes. 



I find that by alterations of the character of the spark this 

 line becomes long and reaches from electrode to electrode. As 

 some of those conditions (such as the absence of the Leyden 

 jars, or the close approximation of the electrodes when the 

 Levden jars are in circuit) are those in which the lines of nitrogen 

 of the air in which the spark is taken are faint or absent, the 

 circumstance of the line becoming bright and long, or faint and 

 short inversely, as the line of nitrogen suggested to me tlie pos- 

 sibility that the line might be due not to the vapour of lead but 

 to some combination of nitrogen under the presence of lead 

 vapour. As, however, this line is bright under similar conditions 

 when the spark is taken in a current of hydrogen, this supcosition 

 cannot be correct. 



A condition of the spark may be obtained in which the strongest 

 lines of the ordinary lead spectrum are scarcely visible, and the 

 line under consideration becomes the strongest in the spectrum, 

 with the exception of the bright line in the extreme violet. 



I need scarcely remark that the circumstance of making use of 

 this line for the purpose of a standard line of comparison is not 

 to be taken as aff jrding any evidence in favour of the existence 

 of lead in the nebulae. 



Each nebula was observed on several nights, so tliat the whole 

 observing time of the past year was devoted to this inquiry. In 

 no instance was any change of relative position of the nebular 

 line and the lead line detected. 



It follows that none of the nebulae observed show a motion of 

 translation so great as 25 miles per second, including the e.irth's 

 motion at the time. This motion must be considered in the re- 

 sults to be drawn from the observations ; for if the earth's motion 

 be, say, 10 miles ptr second from the nebulae, then the nebula 

 would not be receding with a velocity greater than 1 5 per second ; 

 but the nebula might be approaching with velocity as great as 

 35 miles per second, because 10 miles of this velocity would be 

 destroyed by the earth's motion in the contrary direction. 



The observations seem to show that the gaseous nebulae as a 



" Proceedings of the Royal Society, vol. xx. p. 380. 



