52 ELECTRICITY OF SHAVINGS Of WOOD. 



and negative chips four times ; but after laying three or four 

 hours to cool it gave negative chips every time in eight trials. 

 A third piece of cherry-tree that had not been near a fire for 

 four or five days gave negative chips. I repeated thefe ex- 

 periments with different knives that had not very (harp edges, 

 and with beach as well as cherry-tree. And whenever the 

 wood was made thoroughly hot at the fire, it always gave po- 

 sitive chips, not only when hot, but when it was fo cooled as 

 not to be fenfibly warm j but when it had laid away from the 

 fire three or four hours, the chips were always negative. 

 Sometimes when the wood was but (lightly warmed, it would 

 be very difficult to get any figns of electricity, and at other 

 times when the wood was made hot only externally (by putting 

 it very near the fire for a fliort time) the firft few chips would 

 be pofitive, and the fucceeding ones negative. I had one 

 inltanee where with the firft chip the electrometer diverged 

 near an inch, and with the fecond it completely clofed again. 

 Having fucceeded thus far, I thought I would try whether 

 the refults would be the fame if I ufed a very fharp knife, and 

 accordingly (harped two knives on a hone very carefully. And 

 I ufed the fame pieces of cherry-tree made thoroughly hot ; in 

 nine trials with one of the knives, the chips were negative 

 every time and in five trials with the other knife, the chips were 

 negative every time. I made a number of fimilar trials with 

 a piece of beach with always the fame refults, but the beach 

 feemed to be too hard for that keennefs which is neceflary to 

 produce negative chips, for after cutting one or two chips, 

 the edge would be fpoiled, and produce pofitive chips ; but 

 always when the knife was (harped, the firft one or two chips 

 would be negative. Similar to this I found by fubfequent 

 trials to be the cafe with the pieces of cherry-tree, ten or twelve 

 chips of this (which was very ftraight and open grained) would 

 fpoil the edge. 



sluvtogsof dry From thefe experiments it appears, that when very dry 

 wood by glafs, wood is fcraped with a piece of window glafs, the (havings 

 hot wSd b'T are a ^ wa y s pofitively electrified. And if chipped with a knife, 

 moderate fteel .the chips are pofitively electrified if the wood is hot, the edge 

 edge is pofitive, f the knife not very (harp, and negatively electrified if the 

 cold :— and a wood is quite cold. But if the edge of the knife is very keen, 



*ery fharp edge the chips will be negatively electrified whether the wood is 



gives negative , . * , 



whether hot or hot or cold ' 



cold. 2 The 



