on a new Relation between Electricity and Light. 207 



a wooden box 3 inches square and 10 inches long ; a lamp- 

 chimney fixed at the end continued the length another 6 

 inches. 



A stout brass wire, protected by a glass tube where it passed 

 through the mahogany, was fixed along the axis of each pro- 

 jecting box and lamp-glass, and pressed against a little bit of 

 tinfoil pasted on the outside of the strip of wood which held 

 the tinfoil against the glass. A short bit of wire let into 

 the wood connected the small bit of tinfoil with the large one. 

 The whole of the box, side boxes, and lamp-glasses were now 

 filled with the cement already described. About 115 lbs. 

 were used ; it was all melted at once, and poured in. As it 

 was not convenient to warm the mahogany case, the cement 

 was heated considerably above its melting-point, so that it 

 might warm all the wood and glass before commencing to set. 



While it was setting (which took about 4 days) the stair- 

 rods were every few hours removed from the end plugs, and 

 the latter twisted round a few times, and occasionally removed 

 for a few seconds to be re-oiled. 



When the cement was quite set, the plugs were removed, 

 leaving at each end a cylindrical cavity 2 inches deep, at the 

 bottom of which an inch of the edge of the glass could be seen. 

 When these portions of the glass had been cleaned with a 

 little benzine, it was found that an object placed outside one 

 plug-hole could be well seen from the other through the 20 

 inches of glass. 



The skewers which had not been previously touched were 

 now drawn out with some difficulty. The box being laid on 

 its side, one of them previously heated in a spirit-lamp was 

 replaced for a moment, so as to melt the cement at the edges 

 of each hole ; a little fresh cement was now poured in. When 

 it solidified, the holes were completely filled up ; on trying the 

 box with the coil the insulation was all that could be desired. 

 While the poles were connected to the secondary terminals, 

 sparks of 11 and 12 inches were easily obtained between the 

 latter. When the terminals were separated too far for the 

 sparks to pass, the peculiar sound which accompanies the 

 sudden charging of a condenser unable to discharge was heard 

 in the box, showing that neither of the tinfoils had shifted. 



The box was now placed between the Nicols, so that the 

 light passed from one plug-hole to another. Every experi- 

 ment which had been performed with the perforated glass was 

 repeated with the box. Not the slightest effect of any sort or 

 kind was observed on the light. 



It is very likely that I have omitted some precautions taken 

 by Dr. Kerr ; but I do not think that I have omitted any de- 

 scribed in his paper. 



