on a new Relation between Electricity and Light. 205 



thickness can be perforated when the points of the secondary 

 terminals are imbedded in it. When hot it is nearly as liquid 

 as water. The tube and wire were taken up and replaced 

 once or twice, so that the liquid cement might fill every inter- 

 stice. When the cement was hard, the side glasses and corks 

 were removed ; and, the plate being reversed, the second con- 

 ductor was fixed in the same way. 



Next day the experiment was tried. The plate was mounted 

 with its faces perpendicular to the line of light, its conductors 

 horizontal, and its position such that the light passed between 

 their points. The coil was then worked. The insulation was 

 so good that, while wires from each pole were connected to 

 the wires let into the glass, sparks of 12 inches long were 

 easily obtained between the terminals. The coil was worked 

 both with the vibrator and with the clock, with currents con- 

 tinued both for short and long periods, currents in both di- 

 rections both quickly and slowly alternated, and both with and 

 without Leyden jars. 



In not one of the experiments was any effect whatever 

 observed on the light. The compensator was then removed, 

 and, the field being darkened, all the above experiments were 

 repeated. No return of the light or any other effect whatever 

 was obtained. 



But Dr. Kerr has stated that the electrified glass acts like 

 a crystal. Now we know that the action of crystal on pola- 

 rized light increases with the thickness through which the light 

 is transmitted. I thought therefore that if, instead of sending 

 the light through 1 inch of electrified glass, I could send it 

 through 15 or 20 inches the effect produced would be so much 

 increased that, if my having been unable to see it in the 

 former case arose from its smallness and not from its absence, 

 1 should now be able to see it. I therefore had a piece of 

 fine plate glass prepared, 20 inches by 10 and f of an inch 

 thick, and its ends polished. Light passing in at one end and 

 out at the other had then to pass through 20 inches of glass. 

 I then pasted strips of tinfoil 15 inches long on each side, and 

 placed the glass vertical in the line of light. 



I then connected the opposite tinfoils to the secondary poles 

 and worked the coil. No effect was obtained. But only 

 sparks four or five inches long could be used, owing to the 

 electricity springing round the glass. 



It was then resolved to insulate the latter so as to allow a 

 greater stress to be applied to it. 



For this purpose a box was made of inch mahogany, whose 

 inside dimensions were, length 24 inches, depth 16, breadth 7. 

 Two pieces of barometer-tube being fixed horizontally across 



