1879.] L. Schwendler—On a new Standard of Light. 87 
Photometric Measurements. Having now a constant light it became 
possible to measure the variations of light which the combustion standards 
invariably show. 
For instance one of Sugg’s Candles was compared with the P. S. L. 
(A) with the result shown in the following table :— 
Distance in Millimetres. 
REMARKS. 
Teese En (Al , 
with 6.15 Bes. facials CL 
200 mm. 117mm, The P. 8, L. (A) was kept at the same 
120 position = 100 mm. 
g 112 
ral Ss 110 Sugg’s candle was moved in order to get 
& 2 120 the light equal. 
H 120 
ed 120 The variations observed were actually in 
mo 120 the candle and not in the Platinum standard, 
es) 126 as the eye could easily discern, 
ee 128 
2 LEZ 
es, 120 
3 Be. 123 
= 127 
This gives as an average :— 
1 Sugg’s Candle = 1.44 P. 8. L. (A) with 6.15 webers. 
a = — or total variation of the candle about 30 per cent. from 
the average in the very short interval of time of about five minutes. This 
needs no further comment. Some additional experiments were made in 
order to ascertain the variation of the light of a standard candle. 
gives 0.0264 Gm. The resistance of the standard, measured at 66° F., gave 0.143'S. U., 
including contact resistances. 
Now another piece of Platinum sheet 26 x 28 mm. was found to weigh 0.265 Gm, 
The piece cut off which actually becomes hot = 0.026 Gm., which agrees within 
0.0004 Gm., with the weight found by calculation for the P. S. L. (A) actually used: 
Taking the specific resistance of Mercury = 96190 
5 t 0° C 
of Platinum } — 9158 a 
annealed 
the calculated resistance of the Platfaum which becomes hot = 0.109 } Son Wea 
Measured resistance, including contact resistance = 0.143 66° F. 
or contact resistance probably = 0.034 S. U. 
It is therefore much more accurate to define the P. S. L. by weight, than by re= 
sistance, 
