398 Solar Radiation 



for twice 60 consecutive days in the year. The elevation of 

 Kodaikanal is 7000 feet above the sea, therefore the average 

 height of the barometer may be taken to be 585 millimetres 

 and that at Sohag as 760, so that the mass of the atmosphere 

 above the two places is in the proportion 77:100. The 

 maximum rate of distillation at Sohag was 1*5 grams per 

 minute. This is equivalent to i6'6, and after correction to 

 the zenith, to 17*04 grams per square metre. At Kodaikanal 

 the maximum observed rate was 1754 grams distilled per 

 minute. This has no doubt received correction to the zenith, 

 if any was necessary. It is equivalent to 19*39 grams distilled 

 per square metre per minute. 



Multiplying these quantities by the numbers representing 

 the latent heat of steam at 100 C. and 93 C., namely, 535 

 and 542 respectively, we have for the quantities of the sun's 

 radiant heat which have been converted into the latent heat 

 of steam 91 16 gr. C. and 105 15 gr. C. respectively. 



We have still to apply the correction to both observations 

 in order to compensate for the fact that the rays reflected 

 from the outer and inner mirrors do not strike the boiler 

 normally. The effect has been computed to be diminished 

 by this imperfection to the extent of 6 per cent; it is there- 

 fore legitimate to increase both values in the proportion of 

 94 : 100. We thus obtain the quantities 9698 gr. C. and 

 iii86gr. c C 



Conclusion. Considering only my own observations, 

 the final result of the experiments made with my steam 

 calorimeter is that the calorific value of a sheaf of the sun's 

 rays, having a section of one square metre, is at least 

 9698 gram-degrees Centigrade per minute at the terrestrial 

 sea-level ; and it is certain that heat can be obtained from 

 them there at this rate and in a useful form by mechanical 

 appliances of simple construction. 



