36 PHILOSOPHICAL TRANSACTIONS. [aNNO 1770- 



below. It was near midnight and very dark, when he first observed a pale bluish 

 light a few feet above the quarter rail : at first he thought it proceeded from the 

 light in the binnacle; but finding that it frequently disappeared and returned 

 again precisely in the same place, and that it sometimes emitted sparks not un- 

 like those of a small squib, he began to suspect that it proceeded from the con- 

 ductor. To be certain, he ordered all the lights to be put out below, and that 

 no rays of light might issue from the binnacle, he covered it entirely with his 

 cloak. He was presently confirmed in his conjecture, that the light and sparks 

 proceeded from the chain; for, placing himself near it, during the space of 2 

 hours and a half, he saw it frequently emit continued streams of rays or sparks ; 

 sometimes single drops as it were slowly succeeding to each other, and sometimes 

 only a pale feeble light. On examining next morning, he found the chain broken 

 a little above the ship's gunwale, half the eye of each link being quite gone, and 

 the points of the remaining halves about three fourths of an inch asunder ; luckily 

 the chain was fastened to a smaller rope above and below the eye of each link, 

 which prevented that part of the chain below from falling into the water, or of 

 being separated from the part above, beyond the striking or attracting distance. 



XVIII. An Investigation of the Lateral Exposition, and of the Electricity com- 

 municated to the Electrical Circuit, in a Discharge. By Joseph Priestley, 

 LL.D., F.R.S. p. 192. 



Several years before Dr. P. made any experiments in electricity, except with a 

 / view to amuse himself and his friends; he had observed, that in discharging jars, 

 and particularly such as were filled with water, without any coating on the out- 

 side, he felt a slight shock ; though it was plain that the hand in which he held 

 the discharging rod, made no part of the circuit. Mr. Wilson also in his first 

 experiments on the Leyden phial, observed, that bodies placed without the elec- 

 tric circuit vvould be afl^ected with the shock, if they were only in contact with 

 •ny part of it, or very near it. Analogous to this was his observation, that if the 

 circuit was not made of metals, or other very good conductors ; the person who laid 

 hold of them, in order to perform the experiment, felt a considerable shock in 

 that arm which was in contact with the circuit. See History of Electricity, p. 

 95. Lastly, in the course of his experiments with large electrical batteries, he 

 found the force of this lateral explosion, as he calls it, to be very considerable : 

 for he several times observed, that a chain which communicated with the outside 

 of the battery, but which made no part of the circuit, made a black stain on a 

 piece of white paper, on which it accidentally lay, almost as deep as the chain 

 that formed the circuit. (History, p. 644.) And when, in order to judge, by 

 his feeling, of the lateral force of electrical explosions; he made it pass over a 

 part of his naked arm, the hairs of the skin were all singed, and the. papillae py- 



