VOL. LIX.] ' PHILOSOPHICAL TRANSACTIONS. 603 



explosion, passing over his hand, gave it a violent jar, the effect of which re- 

 mained, in a kind of tingling, for some time. 



Lastly, in order to judge the most perfectly of this force. Dr. P. laid a chain 

 communicating with the outside of the battery on his bare arm, above the wrist, 

 and bringing the discharging rod near the flesh, within about 2 inches and a 

 half of the chain, he made the explosion pass over that quantity of the surface 

 of the skin. Had he taken a greater distance, he was aware that the explosion 

 would have entered the flesh ; which, he was sensible, would have given a painful 

 convulsion to the muscles through which it passed. In this case the sensible 

 effect was very different from that, being the same external concussion as before ; 

 and he sometimes thought, that the sensation is not disagreeable. However, the 

 hairs on the skin were singed, and curled up along the whole path of the explo- 

 sion, and for the space of about lialf an inch on each side of it : also the 

 papillae pyramidales of the skin were raised, as when a person is shivering with 

 cold. This was also the case in every part of the arm which the chain touched, 

 and even that part of it which was not in the circuit. Both the path of the 

 explosion, and the place on which the chain lay, had a redness which remained 

 till the next day. Sometimes the flesh has contracted a blackness by this ex- 

 periment, which has remained for a few hours. 



JC. Various Experiments on the Force of Electrical Explosions. By Joseph 

 Priestley, LL. D., F. R. S. p. 63. 



Making the explosion of a battery pass over the surface of a green cabbage- 

 leaf, he observed that it left a track near ^th of an inch in breadth, exceedingly 

 well defined, and distinguishable by a difference of colour from the rest of the 

 leaf. Along this path also the firmness of texture in the leaf was entirely de- 

 stroyed, that part becoming quite flexible, like a piece of cloth. Presently after, 

 it turned yellow, withered, and became perfectly brittle. 



Willing to try the effect of this explosion passing along the surface of other 

 substances, he laid a piece of common window-glass on the path, pressed by a 

 weight of six ounces ; but it was shattered to pieces, and totally dispersed, 

 together with the leaf on which it lay. Placing the blackside of a piece of cork- 

 wood upon it, pressed by a weight of half a pound, the leaf was not rent, but 

 the cork was furrowed all the way, a trench being made in it about half an inch 

 in breadth, and a quarter of an inch in depth. Laying the smooth cut surface 

 of the piece of cork, it was furrowed all the way, as if it had been cut with a 

 file, but not near so deep as before. Many of the small pieces, which had been 

 rubbed oft' in the explosion, remained in the furrow. Also the substance of the 

 cork seemed to be shattered, and it was easily rubbed ofl^, a little way into it. 



He made this explosion on the surface of some red wine, in a small dish, and 



4 h2 



