SURROUNDING MEDIA ON VOLTAIC IGNITION. 
59 
smaller in hydrogen gas than in nitrogen, though both these gases are incapable of 
combining with the terminals ; indeed to obtain an arc at all in hydrogen is scarcely 
practicable. 
Davy has, in his Researches on Flame, given several experiments which are similarly 
explicable ; but though noting the results, he nowhere, as far as I am aware, attri- 
butes them to any specific peculiarity of hydrogen. 
Of the phenomenon which I have examined in this paper, I first published an 
account in connection with some experiments on the application of voltaic ignition 
to lighting mines, and it does not appear impossible that the experiments now de- 
tailed may ultimately find some beneficial application in solving the problem of a 
safety-light for mines. A light which is just able to support itself under the cooling 
effect of ordinary atmospheric air would be extinguished by air mixed with hydro- 
genous gas. 
I am far from pretending to have devised any means of fulfilling these conditions, 
and yet supplying an efficient light ; I merely throw it out as a suggestion for con- 
sideration, knowing that there are no additions to our knowledge which are not 
ultimately valuable in their practical application ; and that a suggestion, however 
vague, — a new point to those whose minds may be occupied with the subject, may 
lead them to results which he who makes the suggestion is unable to attain. 
P.S. Since this paper was communicated I have received a paper from Dr. Andrews 
of Belfast, who published as early as 1840, in the Proceedings of the Royal Irish 
Academy, experiments similar to those of mine first published in 1845. My expe- 
riments were made in the same year as those of Dr. Andrews, but as I withheld 
their publication. Dr. Andrews is fully entitled to priority. Had I known of his 
experiments earlier, I should have recited them in the first part of this paper. 
