88 Mr. J. J. Waterston on some Electrical 



circle -^th of an inch in diameter, and in the exact centre was an 

 excavated cup T jgth of an inch in diameter, as if a hole had been 

 drilled to a very minute depth (fig. 5) . Examined with a watch- 

 maker's lens and reflected light in several directions, it was a 

 simple concavity with bright surface, as if metallic particles, had 

 been torn off. Examined with a microscope magnifying 40 dia^ 

 meters, the cavity was obviously irregular ; there was a slightly- 

 marked ridge round the excavated part, and a few minute speckles 

 of brass outside the rim as if thrown off in a molten state. 



b. Some experiments were made with the view of discovering 

 what became of the small portion of metal torn off at each dis- 

 charging surface. When the discharging surfaces consisted of 

 brass balls coated with wax, the appearance was the same in 

 both, even when one ball was much larger than the other. The 

 electric force in the axis of discharge effectually tore apparently 

 the same number of molecules from each surface ; but in only 

 one instance was there any appearance of those particles after 

 the explosion. In this case one of the discharging surfaces was 

 pointed lead, the other a wax-coated brass ball. A hole was 

 made in the wax coating as before, and about half an inch from 

 it a small patch of brass, about -g^th of an inch in diameter, was 

 found* and in an opposite direction a similar patch of lead. On 

 the other side, at about the same distance from the hole, a small 

 irregular fragment of wax was found adhering, with that pecu- 

 liarity of surface which showed that only the superficial particles 

 had been in a molten state. 



c. When the discharge was repeated by bringing the leaden 

 terminus opposite the hole of the previous explosion, the bright 

 point of the brass ball was found coated with lead ; and a grey 

 powder appeared round the hole in the wax coating, spreading 

 round it to a radius of about half an inch. In this case a brush 

 preceded the spark. 



11. The mechanical effects of the electric explosion between 

 a pointed wire covered with a thick coating of sealing-wax and 

 a naked brass ball were as follows. The coating gave way about 

 three-quarters of an inch from point, with sound of a smart crack 

 of a whip, and the electric fire passed along surface of wax from 

 the fissure to the ball. The fissure extended completely round 

 the coating, but there was no projectile force given to it (fig. 6). 

 The front part of the glove of wax had completely separated from 

 the hinder, but the distance it had moved in consequence of the 

 explosion was imperceptible. 



Description of Electroscope. 



12. The electroscope employed in the following experiments 

 is shown in fig. 7, which is drawn to a scale of one quarter. 



