14 



KNOWLEDGE 



[January 2, 1803 



Las not since been seen, unless possibly once by the late 

 M. Goldscbmidt, of Paris, on the 16th of May, 1855. The 

 orbit of De Vico's comet is very similar (so far as it could 

 be determined by Le Verrier from all the observations 

 available) to that of one discovered by La Hire in 1.678, 

 and it is not unlikely that the comets are identical. It 

 was for some time thought that Finlay's comet might be 

 identical with De Vico's ; but the definitive calculation of 

 Prof. Kriiger (Astrnnomi.scJic Xdchricliten, No. 2781) showed 

 that that view was untenable. The orbits of both comets, 

 however, agree in having very small inclinations to the 

 ecliptic, and perihelion distances from the sun exceeding by 

 only about a sixth part the mean distance of the earth. 

 According to Prof Kriiger's calculations, the period of 

 Finlay's comet is about 6-67 years, so that a return will be 

 due in the summer of 1893. It does not appear that it was 

 ever seen before its discovery in 1886. 



Blackheath, Yours faithfully, 



December 3rd, 1892. W. T. Lynn. 



THEOKY OF THE SUN. 

 To the Editor of IvNo^iiEDGE. 



Sib, — In the excellent noticeof my theory published iu the 

 last (December) number of your magazine. Miss Agnes M. 

 Gierke remarks that if my explanation of the prominences 

 as evanescent illuininations caused by rtijiidbj propaf/iitcd 

 chemical action in tranquil matter viere true, the prominences 

 would give a continuous spectrum. Hydrogen, she says, 

 " ignited by combustion shows no trace of its characteristic 

 lines." That objection, though iu contradiction with a 

 generally accepted statement of Pliicker ("Po.u'g. Ann.," 116, 

 p. 18) that the flame of a mixture of oxygen and 

 hydrogen, when the latter is slightly in excess shows the 

 two lines Ha and H/3, seems at first to be strengthened by 

 a recent note of Prof. Liveing " On Pliu-kerx supposed detection 

 of the Line-Spectrum of Hydyotien in the (Key-hydroi/en Flame" 

 (Fhil. May., Oct. 1892). But the negative results 

 obtained by Prof. Liveing (suppose they prove really that 

 such an eminent observer as Plucker has mistaken lithium 

 and zinc lines for hydrogen) have, I think, no sufficient 

 bearing on the question moved by Miss Gierke. They 

 only prove, says Prof. Liveing himself, " that the tempera- 

 ture of the oxy-hydrogen flame alone is not sufficient to 

 cause hydrogen to emit the rays we sec produced by an 

 electric discharge in that gas." 



If therefore we assume the temperature in prominences 

 higher than in the oxy-hydrogen flames of Prof. Liveing, 

 we see no reason why chemical action should not cause 

 the hydrogen to produce lines there. But there is still a 

 second reason why the remarkable statement of Prof. 

 Liveing has no direct bearing on the constitution of 

 prominences ; and that reason is, that whatever may be 

 the chemical processes in the solar atmosphere (oxygen 

 and water having never been surely detected there), they 

 caimot have any resemblance with the oxy-hydrogen flames 

 tested by Prof. Liveing. 



My explanation of the prominence lines as produced by 

 chemical action is, moreover, strongly supported by the 

 countless well-known observations of lines in flames 

 burning by chemical processes. I need noi insist on that 

 well-established fact, but I only wish to state how 

 unexpectedly the recent work of E. Wiedemann, E. V. 

 Helmholtz, W. H. .Julius, and others on " luminescence," 

 and especially that of E. Pringshcim on the line spectrum 

 of sodium-vapour, have given a strong support to my idea. 

 According to the experiments of W. Siemens (" Wied. 

 Ann.," 18, p. 311) and Prhigsheim ("Wied. Ann.," 45, 

 p. 428, 1892), lieat alone is not xu[licient to cause yases to 

 produce lines ; either electricity or chemical actimi must 



co-operate. No clearer experimental illustration could 

 have been given of the meaning of my theory of the 

 luminous phenomena in the solar atmosphere. 



May I add here that among the numerous observations 

 of prominences published since my theory was written, 

 there are again a great many in close agreement with my 

 theory of a tranquil sun. So, for instance, I found in 

 the " Memoirc della Societa degli Spettrosi Italiani, ' 

 vol. 21, 1892, the description of an enormous prominence, 

 which, according to M. T. Fenyi, could not possibly have 

 been caused by a material eruption or explosion, but 

 seemed to that eminent Hungarian observer produced and 

 very rapidly moving by a sudden and local outbreak of 

 " electricity." 



I finish with an expression of gratitude to Miss Gierke 

 and to you for the trouble you have taken in noticing my 

 theory. Dr. A. Brester, -Jz. 



Delft (.Holland), Dec. 20th, 1892. 



[It seems to me that prominences of the eruptive type 

 afford evidence of actual motion which can hardly be 

 doubted. Not only do we observe very striking displace- 

 ments of the prominence lines in the spectrum which 

 indicate motion of the luminous matter in the line of sight 

 away from or toward-; the observer, but we actually observe 

 rapid motion across the line of sight. The velocity of the 

 motion corresponds roughly with the velocity of a pro- 

 jectile shot upwards under the influence of solar gravity, 

 being sometimes a little more rapid than projectile motion; 

 as we should expect if the matter shot upwards was 

 pa.?sing through a resisting medium, because in being shot 

 upwards it would need to pass through the lower portion 

 of its upward path more rapidly than a projectile moving in 

 free space, which is shot to the same height above the 

 sun. 



I would refer Dr. Brester to papers of mine and of tlio late 

 Mr.Proctor,dealing with the upward motion of prominences, 

 published in the Monthly Xotices of the lioyal Astronomical 

 Society, Vol. XLL, p. 77. On the other hand, the motion of 

 eruptive prominences is sometimes a little slower than free 

 projectile motion would be', probably because the promi- 

 nence observed is either on this side or on the more remote 

 side of the sun's limb, and the matter is not being shot 

 upwards at right angles to our line of sight. If the phe- 

 nomenon observed were due to the mere change in place 

 of electrical illumination, we should expect the velocities 

 observed to correspond with electrical velocities, rather than 

 with the velocities of projectiles moving under solar 

 gravity. On the other hand, the quiescent cloud-like 

 prominences sometimes appear to form, and grow larger, 

 without any visible connection with the 'lower chromo- 

 sphere. It may be that the lines of connection (the stems 

 of the banyan-trees, as Prof. Young aptly calls them) are 

 so faint or thin that we do not notice them, or that there 

 is an electrical or other physical change going on which 

 renders matter luminous that previously existed in the 

 same region in a non-luminous state. 



Dr. Brestsr's letter was received just as Knowi.kdue was 

 going to press, so. that there has been no time to submit it 

 to Miss Gierke. — A. C. R.vnyard.] 



i 



I 



LEMURS. 



By R. Lydekkek, B.A.Cantab. 



N a previous article we have had occasion to refer to 

 Africa as an archaic kind of land containing types of 

 mammalian life which, while formerly widely spread 

 over the Old World, are now restricted to that 

 continent. If this preservation of ancient types be 



