at the total solar Eclipse in 1882. 
71 
First of all it must be remembered that the calorimeter is 
efficient only when it is running continuously and at or nearly at 
its full load. In the case of a total eclipse there must be an 
interval during which the sun cannot keep steam however 
large the reflector may be and however great its condensing 
power may be. We have seen that when exposed cold as 
soon as possible after the total phase of the eclipse, it was 27 
minutes after totality before the water boiled. One third of the 
sun was then uncovered. It is therefore reasonable to suppose 
that, if the eclipse had happened at noon so that the first half 
of it could have been utilised as well as the second half, the sun 
would have kept steam in the calorimeter and it would have 
continued to distil until two thirds of the sun’s surface had been 
obscured. Then distillation, if it did not cease, would become so 
slow that its rate would have no value, and fifty-four minutes 
would elapse before one third of the sun would again be uncovered 
during which the calorimeter would get cold. During this 
interval steam must he kept artificially. This is very easy. The 
glass tube which forms the steam dome is attached to a metal 
collar which screws down on a washer. It can therefore be easily 
detached. If then the steam tube of the calorimeter be connected 
by means of an india-rubber tube with a flask in which water is 
kept boiling, steam can be passed through the calorimeter at the 
normal rate until it is judged suitable to expose it again to the 
sun. There is no difficulty about this. It might however be well 
for use during an eclipse to provide increased reflector power. 
But it would be necessary to shade it with a diaphragm when 
used with the uneclipsed sun, and the comparison of the heat of 
the eclipsed sun with that of the uneclipsed sun would be defec- 
tive. Fortunately the power of varying the constants of the 
instrument is so great that one or two trials would suffice to fit it 
for use during an eclipse. 
Although quite insignificant as a natural phenomenon an 
annular eclipse is better for calorimetric experiments than a total 
one. Next year on 11th November there will be an annular 
eclipse visible in Ceylon. The annular phase will last over ten 
minutes and at its greatest 0875 of the sun’s disc will be covered. 
It is pretty certain that the calorimeter used in 1882 would not 
keep steam through this phase, but a larger reflector might be 
used. It would be worth while to have a reflector of such a size 
that steam would certainly be kept through the whole eclipse, 
especially during the annular phase when all the radiation is from 
the peripheral region. 
