243 REPORT — 1875. 



I. II. III. TV. V. 



At 100°. At 250°. ^'1°'', ^^I'^'l ^S*'''^, 



red heat, red beat. red heat. 



Carbonic acid 95-46 ... 92-33 ... 42-27 ... 35-82 ... 550 



Carbonic oxide 0-00? ... 1-82 ... 5-11 ... 049 ... 00 



Hydrogen 4-54 ... 6-86 ... 4806 ... 58-51 ... 87-53 



Kitrogen (calculated) 000 ... 000 ... 4-56 ... 5-18 ... 6-01 



100-00 100-00 10000 10000 100-00 



As regards the gas they occlude, iron and stony meteorites sho-R^ a marked 

 distinction. While the gases of the Lenarto iron contained 85'68 per cent, of 

 hydrogen, those obtained from cosmical masses of the stony kind, if the Iowa 

 meteorite may be regarded as a type, are characterized by the presence of car- 

 bonic acid, Avhich constitutes nine tenths of the gas evolved at a temperature 

 of boiUng water, and about one half of that given off at a lo-^v red heat. 



The spectiTim of the gas of the lo-wa meteorite, when the pressure of the 

 pump -was high, gave very brilliant carbon bands, the hydrogen lines being 

 wcalv and comparatively inconspicuous, although at a very lo-^v pressure they 

 became relatively stronger. The brightest carbon bands -were the three in 

 the green and blue, the red one being much feebler. These are precisely the 

 ones most conspicuous in the spectra of some of the comets ; and this fact is 

 a remarkable confirmation of the received theory as to the meteoric character 

 of those bodies. 



This, moreover, is a very significant fact in sho-wiug that it is quite unneces- 

 sary to assume the existence of volatile hydrocarbons to explain comctary 

 spectra, as some -writers have done, and that the presence of the t-vvo oxides 

 of carbon in such quantity is quite sufficient to account for all that has been 

 observed -when we consider the circumstance that the tension of the gases of 

 the cometary appendage must be extremely small. Were a largo comet to 

 approach near enough to the sun to have its nucleus intensely heated, it is 

 lug-hly probable that, over and above the bands already observed, the hydro- 

 gen lines -would be found in its spectrum. 



AVright expresses regret that such a comet as Donati's should have departed 

 into space just early enough to escape observation with the spectroscope. 

 While the most probable cause of the emission of light under these conditions 

 is electricity, another may be found in the property of gaseous bodies of 

 emitting light of the same character as that which they absorb. It is not 

 altogether improbable, Wright suggests, that the solar radiations absorbed by 

 the gaseous matter, although for the most part converted into heat, would also 

 in part be emitted again as light, and that in the case of volumes of gas filling 

 many cubic inches, the intensity might be sufficient to give a distinct spectrum 

 of broad bands or lines, even though, on the scale of any possible experiment, 

 no trace of such an action can be detected. These researches have led the 

 author to accept the follo-yving conclusions : — 



1. The stony meteorites are distinguished from those which are metallic by 

 occluding the oxides of carbon, chiefly carbonic acid, as their characteristic 

 gases, in place of hydrogen. 



_ 2. The proportion of carbonic acid evolved is much greater at low than at 

 high temperatures, and is sufficient to mask the hydrogen in the spectrum. 



3. The amount of gas contained in a large meteorite, or a cluster of such 

 bodies ser-ving as a cometary nucleus, is sufficient to form the train as ordi- 

 narily observed. 



4. The spectrum of these gases elofiely resembles that of several of the 

 comets. 



