and Surfaces of Incandescence Lamps. 375 
larger collection of statistics is obtained we shall not be in any 
position to determine if these constants are definite for each 
type of lamp or kind of carbon, and whether the average life of 
a lamp can be predicted from a knowledge of these constants. 
An attempt was made, in the next place, to endeavour to 
obtain an approximate empirical formula connecting the 
efficiency of a lamp, or the candles per horse-power, and the 
electromotive force. On April 13, 1882, Prof. A. Jamieson 
read a paper before the Society of Telegraph Engineers and 
of Electricians (Journ. Soc. Tel. Eng. vol. xi. p. 164), “On 
Tests of Incandescent Lamps,’ and he has there given a 
number of tables and curves for different lamps, giving the 
efficiencies and resistances for various electromotive forces. 
These observations afford a convenient means of putting to 
the test empirical formule, because the observations seem to 
have been carried out with very great care, and being done 
with secondary and primary batteries as current generators, 
the observations are more likely to be accurate than when a 
current from a dynamo machine is used; also because the 
observations for candle-power were entrusted to Dr. Wallace, 
gas-analyst for Glasgow, and were therefore in the hands of 
an observer whose eye was probably more trained to detect 
minute differences of illumination than one not so familiar 
with such work. 
Professor Jamieson gives one complete table of the constants 
of an Edison 8-candle lamp over a great range of candle- 
power. Selecting that portion of the table in which the 
electromotive force was high enough to illuminate the lamp, 
we have as follows :— 
TaBieE III. 
Tests of an Edison 8-candle Lamp, made by Prof. Jamieson, 
March 8, 1882. 
- H.M.F. Current, | 
aaa in volts, in amperes, Cancie power, 
V. A. | 
. 63°7 45-9 0-722 52 : 
63:3 46-7 0-737 6-2 | 
62°7 48°3 0-77 8-2 | 
61 51:9 0°85 129 | 
60-6 53 0-874 14:3 | 
59°3 56-2 0-948 21:3 | 
58-4 58 0:995 25-3 
578 61:1 1:06 35:8 
57 63°1 | 1-21 43°8 | 
= | 
If we take the logarithms of these numbers we have the 
following table :— | 
