TRANSACTIONS OF SECTION G. 1197 
Contact is made and broken within a small cavity in the switch plate containing 
a single drop of oil, Even without this precaution, there is not the slightest danger 
of ignition of explosive gas by a spark produced at the switch on opening the circuit. 
To charge, say five hundred lamps would neither be complicated nor costly ; a 
dynamo absorbing three to four H.P. would suffice. The cells would be ranged on 
benches in front of fixed wires from the dynamo; and these would be so fitted 
with coupling plugs, that the connecting of several hundred batteries would be the 
work of a very short time. 
The cost of the renewal of the electric would probably be about the same as the 
cost of filling, cleaning, and keeping in repair Davy lamps; or about 2d. per lamp 
per week. The supply of oil for ordinary safety lamps costs another 2d. per week ; 
which would fully cover the cost of charging the batteries for the electric light. 
Here, then, is a miner’s lamp, to which the appellation of ‘ Safety’ may be given 
without any reservation; and one which is free from even the suspicion of causing 
an explosion of fire-damp. [Besides its safety, there is one other advantage of 
occasional importance. Oil lamps require air more or less pure to support the 
combustion of the oil, There are, unfortunately, times, after an explosion of fire- 
damp, when the air of the pit is so foul that no oil lamp will bum init. With 
this electric lamp, which requires no air, and with a Fleuss apparatus for breathing, 
the work of exploration might be carried on, and this, it is reasonable to hope, 
would be attended with the saving of life. 
3. On the Strength of Telegraph Poles. By W. H. Preuce, F.R.S., 
M.Inst.0.L.—See Reports, p. 853. 
4. On Domestic Electric Lighting. By W. H. Prences, F.R.S., M.Inst.C.B. 
After referring to the full details of the lighting installation of his house in 
Wimbledon, given to the section, at the meeting at Montreal, Mr. Preece referred 
generally to the experiences he had gained during the past twelve months. ‘The 
secondary batteries, upon which he had mainly relied, exceeded his expectations in 
the services they rendered. They returned 70 per cent. of the energy put into 
them, without any apparent diminution whatever in their E. M. F. They showed 
no signs of deterioration and gaye no trouble whatever. He used his gas engine 
for charging only two days a week. He had experienced no fault with the wiring 
of his house. He had used only the very best materials, and had attended person- 
ally to the insulation of the system. It was periodically tested and found to be 
good. He referred in severe terms to the cheap and nasty wire, which was so fre- 
quently and ignorantly used, and feared that the prejudice against the electric light 
would increase when failures from this cause arose. None but the very best ma- 
terials should be used, and the joints should be seen to by experts. 
He had devoted considerable attention to the problem of distributing light, 
and had succeeded so far that, while his rooms were beautifully illuminated, the 
eye was not irritated by regarding a bright source of light. The lamp he used was 
a 50-volt 10-candle power glow lamp, and it was, as a rule, so fixed that the eye 
never saw it. He had arrived at the use of these lamps after careful consideration 
and many trials of other lamps. They secured greater safety in the leads, and in- 
volved less capital in batteries through the use of low E. M. F. 
He ran his lamp at an E. M. F. about two per cent less than the nominal 
E.M.F. He did this to secure long life to his lamps. The breakage had been 
very small. The E. M. F. and current which will give a lamp a normal life of 
1,000 hours and a certain candle power, should be determined by every maker. 
The sixth power of the current will give the candle power, and the twenty-fifth 
power the life with any other current. The great advantage of batteries is, that the 
proper current once determined, can never be exceeded, and thus efficiency is en- 
sured. If lamps are run too low, there is waste of power; if too high, there is 
waste of lamps. We are now gradually acquiring a thorough knowledge of the 
