502 M. F. Brann on the 
example cannot be completely converted into electrical energy 
(with an oppositely bent curve it would not be the only equi- 
valent), but there would be also heat from the interior of the 
metals themselves converted into work. 
The following Table II. gives for different intervals of tem- 
perature the heat Ilg—IIg in gramme-calories. Further, the 
electrical work L in the same units. The result is that in 
the most favourable case 47 per cent. of the heat Ig—IIy 
appears as useful electrical work. The remainder, at least 53 
per cent., remains in the metals themselves, in the form of 
(reversible) heat. It is given in the fourth column. 
The thermopile absorbs the quantity of heat Io at the 
highest temperature ©; at least, the pile works with this 
heat-capital, How much of this heat appears as useful work ? 
The sixth column shows that it is at the outside 40 per cent. 
If of the quantity of heat IIe the whole remainder not con- 
verted into work at the temperature @ were given off, the 
. O-90 ‘ 
fraction 6 must be converted into current-energy. The 
next column shows this fraction, 
Tasxe II. 
Elec 
‘Temp. Pelle work, II og LOS ea L | 60—@ |Te—Te 
interval. Jap ey ete el = Uliga malig S) Ile 
20-100 36°8 15°8 21:0 0:43 0-19 | 0-21 0°44 
20-200 107°5 42-7 64:8 0:40 0:28 | 0:38 0:70 
20-300 | 198-4 79°4 119-0 0-40 0:32 | 049 | O81 
20-400 | 272'3 128°5 149°8 0:47 0-40 | 0°56 | 0°85 
20-500 402-1 174:0 228°1 0-43 0°39 | 0-62 0°89 
20-600 | 705°7 229°2 476°5 0°32 0°30 | O66 | 0:94 
If we now enquire whether thermo-elements are suitable 
arrangements for converting heat into work, we obtain the 
following result :—Elements for which the electromotive 
force increases greatly with rise of temperature, as is the 
case for the element HgPb, work with very small useful 
effect (not regarding the loss of heat by conduction, radiation, 
&e.). Thermo-elements whose electromotive force decreases 
with rise of temperature work with more useful effect, but 
contribute absolutely less towards the work to be done. 
Other elements with liquid metals give essentially the same 
results as the PbHg element. The curve for Hg(Hg + Br + Pb) 
has nearly the same form. In this combination both con- 
stituents are fluid at ordinary temperatures ; I have examined 
them for an interval of more than 500°. It appeared to me 
