DISCHARGING OF ORDNANCE. 



517 



Another cause may be assigned for the gunpow- 

 der at the joinings a, b or c, remaining uninflamed. 

 There is scarcely any air contained in the space 

 a,b or c ; the flannel and gunpowder nearly fill 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 fexist 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 con- 

 tained in the tube, and therefore promote the ac- 

 tion ; or when we leave a quantity of air at a 9 b, or 

 c 9 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 often 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 disengagement ; but, 

 when it meets with resistance, in contact with such 

 substances, or when it is presented to them in its 

 nascent state, then its full energy may be displayed, 



