S. P. Langley—The Actinic Balance. 197 
All are given here exactly as they were obtained, except one, 
bey involved an obvious error, but this one equally indicated 
eat. 
Actual deflections (heat), 
53 
28 
West limb | 53 
Balance cover open. Bal- | enters first. { 56 
44 
moving the telescope by 
hand. 
enters first. | 30 
5 
2 
Balance covered except during exposure } 23 
and image kept in the same position at all } 41 
times by the equatorial clock. 27 
51 
Mean deflection = 41°6 + 2°4. (Prob. error of a single observation = 9°9). 
The preceding measures on lunar heat will doubtless be im- 
proved on. They are the first taken and are given here not for 
any intrinsic value of their own, but as aids in judging the 
capacity of the balance, to not merely indicate, but measure 
orms of radiant energy hitherto supposed beyond reach; for I 
am not aware of any previous authentic measures of the lunar 
a which have passed through the glass lenses of a refracting 
telescope. 
energy (as it reaches us through our atmosphere), is nearly at 
its minimum precisely where the so-called “actinic” curve is 
