311 
Combining this with (1), we obtain as a more accurate 
formula, 
Potential-difference to employ with Incandescent Lamps. 
ayaa On OB) eree (8) 
But unfortunately this more accurate formula does not 
lend itself to mathematical calculation, whereas that given in 
(2) is very suitable for this, and has a sufficient degree of 
accuracy for our purpose. In using (2) we are really using 
for the candle-power 
O(v) = 1008455 0—2'303 (5) 
instead of (1). 
It will be also found that from 95 to 105 volts, the range 
of volts given in Table II., the values of ¢(v), or watts per 
candle-power, when corrected for errors of observation, satisfy 
with considerable accuracy the equation 
d(v) —3-7 + 1 (Q8:007—0°07667 o (6) 
If, however, we take the whole range of values given in 
Table I., then it will be found that the equation 
b(v) = 2 + 104424008798 » 
is better satisfied than (6). 
The following Table III. gives the numbers we have actually 
employed in making these calculations. 
TABLE III. 
| sya | Waits per 
v. V/ (0). a(v) Watts candle-power| log {¢(v)—2}. 
corrected. | corrected. | corrected. 4(0) 
84 1-4 2°744 56 20-408 1:2650 
86 ia 3°582 60°15 16°79 1:1700 
88 1:66 4-574 64°25 14:27 1:0888 
90 1-786 Sef 68°4 12:0 1:0000 
92 1-914 70 726 10°37 °9227 
94 2:044 8°55 76°85 9-0 *8451 
96 2-75 10°28 81 7882 "7695 
98 23 12-167 85°15 70 6990 
100 2°428 14:24 89:3 6271 *6305 
102 2°556 16°69 93°5 56 "5563 
104 2°682 19:29 97°8 5:07 ‘4871 
106 2°81 22°188 101-9 4°593 ‘4138 
108 2°94 25°412 106 4°172 3369 
110 3°065 28°79 110-1 3°824 -2610 
112 3195 32°61 114:25 3°504 1772 
114 3°32 36°594 . | 118°3 3°233 0910 
Using (6) and (2), the total cost of one candle per year is 
é H 
0°07545 p—11697 7 8-007 —0-07667 v 
prio + agg (8-7 +10 \s 
