1882.] 071 Comets. 7 



through the mass. This meteorite gave off about two and a half 

 times the volume of the meteorite as a whole, or twenty times that 

 of the iron scattered within it. The same gases came off, but in a 

 different proportion ; there being a larger proportion of the oxide of 

 carbon, at a low temperature carbon dioxide was chiefly given off.* 

 Now in all these cases, a spectrum similar to that of comets would 

 be given by these gases under suitable conditions. 



Some years ago, in conjunction with my friend Professor Maskelyne, 

 I examined the spectra of certain meteorites, and obtained in several 

 cases a spectrum similar to that of comets. Some meteorites like that 

 of Bokkveldt, contain a large percentage of hydrocarbons. Professor 

 Vogel has recently experimented in the same direction, and finds that 

 the gas which comes off from the meteorite he used gives a hydro- 

 carbon spectrum mixed with that of carbonic oxide, and under certain 

 conditions the spectrum of hydrocarbon predominates and becomes 

 almost exactly similar to that of comet h 1881.t We are at a dis- 

 advantage in one particular, for we cannot get at meteorites as they 

 exist in celestial space, but only after superficial ignition in passing 

 through the air. 



The experiments hitherto made throw but little light on the 

 question, whether cyanogen ready formed is present in combination 

 or otherwise in the comet, or whether it is formed at the time by the 

 interaction of carbonaceous and nitrogenous matter. In the latter 

 case we should have to admit a high temperature, which would be 

 in favour of the view of an electric origin of the comet's light. 

 Professor A. Herschel and Dr. Von Konkoly have pointed out that the 

 spectra of the periodic meteors are different for different groups. I 

 may also mention that Captain Abney considers that he has evidence 



of hydrocarbons in the outer portion of the sun's atmosphere. 



» 



* ' American Journal of Science and Arts,' vol. x. July 1875. 

 t ' Publicationen des Astrophysikulischen Observatoriums,' Band ii. p. 182. 

 Since this Discourse was given, Dr. Flight has presented to the Eoyal Society 

 a paper on the Meteorite of Cranbourne, Australia, and the Eowton Meteoric Iron. 

 In the case of tlie former, the occluded gases amounted to 3*59 the volume of 

 the iron, and consisted of — 



Carbonic acid 0*12 



Carbonic oxide 31 '88 



Hydrogen .. 4.5-79 



Marsh gas 4 • 55 



Nitrogen 17 'GG 



100-00 



The Eowton Iron gave 6*38 times its bulk of gas, as follows — 



Carbonic acid 5-155 



Hydrogen 77-778 



Carbonic oxide 7 ' 345 



Nitrogen .. ., .. 9-722 



100-000 



