VOL. XLVII.] PHILOSOPHICAL TRANSACTIONS. 21d 



showing the great quantity of electricity in the clouds. And had there been a 

 good wire communication from the spintle heads to the sea, that could have 

 conducted more freely than tarred ropes, or masts of turpentine-wood, he ima- 

 gines there would either have been no stroke, or, if a stroke, the fire would 

 have conducted it all into the sea without damage to the ship. His compasses 

 lost the virtue of the loadstone, or the poles reversed, the north point turning 

 to the south. By electricity we have here frequently given polarity to needles, 

 and reversed it at pleasure. Mr. Wilson tried it with too small a force. A shock 

 from 4 large glass jars, sent through a fine sewing needle, gives it polarity ; and 

 it will traverse when laid on water. 



If the needle, when struck, lie east and wests the end entei-ed by the electric 

 blast points north. If it lie north and south, the end that lay towards the north, 

 will continue to point north, when placed on water, whether the fire entered at 

 that end, or the contrary end. The polarity is given strongest, when the needle 

 is struck lying north and south ; and weakest, when lying east and west. Per- 

 haps if the force was still greater, the south end, entered by the fire, when the 

 needle lies north and south, might become the north ; otherwise it puzzles us 

 to account for the inverting of compasses by lightning ; since their needles must 

 always be found in that situation, and by our little experiment, whether the blast 

 entered the north, and went out at the south end of the needle, or the contrary, . 

 the end that lay to the north, still should continue to point north. 



In these experiments the ends of the needles are sometimes finely blued, like a 

 watch spring, by the electric flame. This colour given by the flash from 1 jars 

 only, will wipe off"; but 4 will fix it, and frequently melt the needles. Some- 

 times the surface on the body of the needles is also run, and appears blistered, 

 when examined by a magnifying glass. The jars Mr. F. used held 7 or 8 gal- 

 lons, and were coated and lined with tin foil. Each of them takes 1000 turns 

 of a globe Q inches diameter to charge it. He sent 1 specimens of tin foil melted 

 between glass, by the force of 1 jars only. 



, I have not heard, says he, that any of your European electricians have been 

 able to fire gunpowder by the electric flame. We do it here in this manner : 

 a small cartridge is filled with dry powder, hard rammed, so as to bruise some of 

 the grains. Two pointed wires are then thrust in, one at each end, the points 

 approaching eacii other in the middle of the cartridge, till within the distance of 

 half an inch : then the cartridge being placed in the circle, when the 4 jars are 

 discharged, the electric flame leaping from the point of one wire to the point of 

 the other, within the cartridge among the powder, fires it, and the explosion of 

 the powder is at the same instant with the crack of the discharge. 



