S8S Mr Deuchar on the Nai/are of Flame. 
tiori of the flame. We are entitled to draw this conclusion from 
the phenomena which occurred in the 1st, 8th, and 10th expe- 
riments ; in these we found that the flame did not act upon the 
substances through which it passed when the resistance was 
feeble. But in the 9th and 10th experiments, when the resist- 
ance to which it was opposed was increased, then its effect upon 
. the substances was more apparent. The same change of effect 
seems also to take place with regard to the gunpowder ; when 
the resistance is increased, the powder is always inflamed, and 
the apparent inertness only takes place when the motion of the 
flame is left almost wholly free. The failure of effect alluded 
to in several of the trials in the 24th experiment, may have oc- 
curred from the flannel having been too thick and compact, or 
from too large a body of flame having passed down the tube at 
one discharge. 
Another cause may be assigned for the gunpowder remaining 
uninflamed. There is scarcely any air contained in the spaces 
h and c ; the flannel and gunpowder nearly All the whole, so far 
as the tube is unscrewed, and the tube itself contains little air. 
Now, a certain quantity of air may be necessary to enable the 
caloric, in the insulated and condensed form in which we may 
assume it to exist during this rapid motion, to display fully its 
usual effects upon substances. When this supply of air is not 
present, then the caloric passes through the gunpowder and 
other substances without inflaming, or otherwise affecting them; 
but when we put resistance at the bottom B, we facilitate the 
concentration of the air contained in the tube, and therefore 
promote the action ; or when we leave a quantity of air at «, 5, 
or c, we in like manner assist the inflammation. 
The above explanation will appear in a still clearer point of 
view, when we consider the nature of those affinities which of- 
ten take place between bodies, when in a nascent state, although 
every attempt has failed to unite them, after they have assumed 
their separate forms. The same may occur with regard to 
flame. When propelled in an insulated form, it may not act 
upon inflammables placed at a distance from the point of its dis- 
engagement ; but, when it meets with resistance, in c^ontact with 
such substances, or when it is presented to them in its nascent 
state, then its full energy may be displayed. Its effects, there- 
