1879.] L. Schwendler—On a new Standard of Light. 93 
In conclusion it may be stated that it was ascertained that the Plati- 
num Light Standard (B) produced the unit intensity of light, (the unit of 
light equal to the light emitted by the Standard Candle) at a total expen- 
diture of energy equal to 427 © ergs per second. Of these, 300 Q ergs 
were actually transformed into light by heating the platinum up to a high 
temperature ; while the remaining 127 Q ergs were lost for illuminating 
purposes, being used for raising the temperature of the circuit exclusive 
of the Platinum Standard. 
The Platinum Light Standard (A) being made of much thicker plati- 
num sheet, showed a much less favourable result. The unit of light by 
(A) was produced at a total expenditure of energy equal to 1226 © ergs per 
second, of which 725 © ergs were actually transformed into light, the 
remaining 501 Q ergs were wasted in heating the circuit to low tempera- 
ture (no light). Considering that the unit of light can be produced in 
an electric are at a total expenditure of energy of 10 Q ergs per second 
only (see my Précis of Report on Electric Light Experiments, London, 
1st Nov. 1878, p. 11), when produced by Siemens’s intermediate Dynamo- 
Electric Machine, it follows that from an engineering point of view, 
light by incandescence can scarcely be expected to compete with light 
by disintegration (electric arc). 
In fact, it appears that light by incandescence is scarcely any cheaper 
than light by combustion. The reason for this is that the temperature of 
an incandescent platinum wire is not very much higher than the tempera- 
ture of a flame, and that for unit volume the mass which has to be kept 
up heated in a piece of platinum is much larger than the mass in a flame. 
Unless we should be fortunate enough to discover a conductor of electricity 
with a much higher melting point than platinum, and that the specific 
weight and specific heat ef that conductor is also much lower than 
for platinum—and that at the same time the new conductor does not 
combine at high temperatures with oxygen, we can scarcely expect that 
the principle of incandescence will be made use of for practical illumination. 
Further it was ascertained that the resistances of the platinum light 
standards (not including constant resigtance) were as follows :— 
P. LS. (B) = 0°186 Ohm at 22:2? C. 
= 0876 ,, at the temperature of the standard, 
0'876 
0136 — 6:44. 
Pais 8. (A) = 0°102 Ohm at 18-9° C. 
= 0964, ,, at the temperature of the standard, 
964 
G10, 2 
where the light was measured, or increase 
are 
_ where the light was produced, or increase 
12 
