/8o LIGHT SCIENCE FOR LEISURE HOURS. 



subjected to spectroscopic analysis, so that we cannot 

 pronounce with any certainty respecting the structure 

 of these singular appendages. Some astronomers are 

 disposed to look on the formation of a track of meteors 

 all round the orbit of a comet as due to the action of 

 influences by which parts of the comet's mass are 

 thrown into orbits of slightly longer period than that 

 of the head, though closely resembling that orbit in 

 figure. Be this as it may, it is certain that the great 

 contrast in character between the meteoric bodies 

 which form the train of a comet, and the gaseous 

 nucleus and coma, remains yet among the mysteries 

 which astronomers have been unable to clear up. 



But so soon as it had been shown that a comet's head 

 is formed of a certain well-known terrestrial substance, 

 it was natural that the question should be asked 

 whether this substance is to be found in meteors. 

 Hitherto no great progress has been made in deter- 

 mining the elementary constitution of meteors which 

 have not actually fallen upon the earth. It is so diffi- 

 cult to catch them during their brief transit across our 

 skies that only a few substances, as sodium, phosphorus, 

 magnesium, and so on, have been shown with any 

 appearance of probability to exist in shooting-stars. 

 Certainly carbon is not among the number of those 

 elements which have been detected in this way. But 

 at a recent meeting of the Astronomical Society, it was 

 stated that several aerolites contain carbon in their 

 structure, and Dr. De la Rue offered a fragment of 

 one of these to Dr. Huggins for analysis. Certainly a 



