48 H. Haug on the Electro-motive Force 
is 8-21; the mean of the last three values of the same column 
is 6°34. The increase is in the ratio of 1 to 1-975. Leaving out 
the value of column (0), as too low, but taking the mean of the 
six mean values to the left of column (0), from 17- st to 23-03 
there being three small and three large values, we get an in- 
crease of internal resistance from 3°21 to 18 ‘51, or Pin 1 to 5°77. 
This increase is due to the reduction of intensity from 1°3422 to 
0-0581, and to the reduction of temperature of the unit of resis- 
tance, from dark red heat of the 6 cm. of platinum wire, to 
about the temperature of the air. 
It may be well to examine with some detail this series of ob- 
servations. The battery was in such a state that the direct inten- 
sity decreased rapidly during the short time necessary for 4 pairs 
of observations of the n eedle. The intensity artes any length of 
platinum wire in the circuit, was variable too, oming dimin- 
ished with short length, and increased with great adett of the 
wire. The examination of the following figures will give an 
idea of the amount of this variation of intensity. They are the 
mean values for the first, respectively for the second two pairs of 
Cent. of plat. Intensities. Cent, of plat, Intensities. 
wire in the r —~ ~ wire os e 1e -——— oT 
circuit. First. Later. circu First. Later. 
1:5039 1:3605 nm 1437 1441 
6 4679 4665 60 1267 1259 
8 4119 4097 70 1118 1130 
10 8721 8729 80 1000 1016 
12 3402 3424 90 0898 0919 
14 3177 8153 100 0814 0840 
16 2929 2934 110 0748 OTT4 
18 2762 2783 120 0705 0726 
20 2594 2596 130 06 0677 
30 2052 2048 140 0608 0634 
Oi shed bea 0567 0585 
instead of the above values 3°21 and 6:34, ais an scoot om 
1 to 5. The true ratio of increase i refore somewhat 
less shins calculated from the table, and this cau good for the 
whole ratio of increase. 
On the a hand, if the decrease of intensity with the time, 
mainly to assigned, as probably will be maintained, to some 
me ae ceca taken fs which, from the high direct in- 
tensity to the next with 6 em. of platinum wire in the circuit, 
will be kept for some time near its maximum; then the inten- 
sity with 6cm. of rheochord wire is lower than it would be, 
had the circuit not been closed, directly and constantly, previous 
to the observation with 6 cm. of platinum wire, since this low 
