i 879«] Proceedings of Societies . 261 
each of which supplies four distindl lamps, making a total of 
twelve lights. The American Brush machine was also men- 
tioned. The Dubosq lamp, which was the first regulator, is 
well adapted for laboratory purposes, but for practical purposes 
the Serrin is preferable. Rapieffs lamp is used in the Times 
office. The De Mersanne, which was highly spoken of at the 
Paris Exhibition, moves the carbons by bevelled gearings. The 
Wallace-Farmer lamp, though durable, is unsteady, perhaps 
because only inferior gas carbon has yet been used. Jablochkoffis 
candle was found to be defective from the solid insulator, such 
as plaster, used between the carbon. This made it very expen- 
sive also. Experiments in Paris had shown that whereas 
Jablochkoff’s system cost iod. per hour per light, the other 
systems cost only one half of that. In Wilde’s candle the solid 
insulator was dispensed with, air taking its place, the arc always 
tending to keep at the top of the candle by electro-dynamic 
repulsion. In the De Meriten’s candle three strips of carbon 
were used, the intermediate one being a stepping-stone to the 
arc which passes between the two outer ones. Werdermann’s 
and Reynier’s so-called incandescent lamps were also shown. 
Mr. Shoolbred, after alluding to the facft that the upper (posi- 
tive) carbon takes a crater form, and hence becomes a refledfor 
shedding the light downwards, stated that experiments had 
proved the line of maximum intensity of light to pass downward 
at an angle of 6o° to the axis of the vertical carbons. By giving 
the positive carbon a horizontal displacement behind the lower 
negative one, Mr. Douglas, of the Trinity House, had been able 
to raise this line till it became horizontal, an advantage in light- 
houses. He also pointed out that, whereas in Paris the Jabloch- 
koff waxed for a period short compared to that in which it 
waned, in London it waxed for longer than it waned, which was 
of course an improvement ; and Mr. Shoolbred suggested that 
it might be due to the fadt that the engine worked at a speed 
nearer to that of the machine, and that the machine was founded 
more solidly in London than in Paris. 
In the discussion which followed the reading of Mr. Shool- 
bred’s paper, 
Mr. Werdermann maintained that it was as easy to produce 
500 lights as 10 from the eledtric light by sub-division, as he 
hoped soon to show, and stated that the size of the carbons 
greatly controlled the intensity of the light. 
Prof. Ayrton held that the obstacle to the sub-division of the 
eledtric light was not an eledtrical one, but was due to the fadt 
that the amount of light produced by the current is not in diredt 
proportion to the amount of the heat produced. 
Prof. Silvanus P. Thompson pointed out that residual mag- 
netism in the cores of the bobbins of dynamo-eledtric machines 
lowered their efficiency, and hence short cores, as in the Wallace- 
Farmer machine, were an improvement. 
