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 be 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 0"875 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. 



