at the total solar Eclipse in 1882. 



67 



to consider the rates observed at other times during the three 

 days and the following table, which gives the amount of water 

 distilled in each hour in the different days, may be used. 



If the experiments were to be repeated, I do not know in what 

 particular the conditions of weather, as they were on the forenoon 

 of the 18th, could be made better. Yet if we admit that they 

 might be improved in the proportion that the conditions between 

 10 and 11 a.m. on the 18th are better than those obtained 

 between the same hours on the 16th, when they were the most 

 unfavourable, the rate would have to be increased in the proportion 

 58 - 8 : 82*4 and it would become 15 x 14 = 21 c.c. per minute. 



Time 



Cubic centims. water distilled 



from to 



16th 



17th 



18th 



A.M. 









9 10 







78-1 



10 11 



58-8 



70-25 



82-4 



11 12 



69-5 



69-7 



82-8 



P.M. 









2 3 



73-2 



65-5 



71-6 



3 4 





57-9 



64-8 



This correction is certainly too great when considered as an allow- 

 ance for faulty weather, and even if held to cover all instrumental 

 deficiencies, such as imperfect equatorial adjustment and others, 

 I believe it will be still much in excess of the truth ; moreover, 

 I am convinced that if the calorimeter furnished steam at this 

 rate it would be in such conditions that it would be impossible 

 to stand by it and attend to it on account of the excessive heat. 



Having thus indicated the maximum correction which can 

 be applicable to our observations we return to the consideration of 

 the observations themselves, where we are on the sure ground of 

 experiment. 



In the circumstances we may, without sensible error, take 

 the cubic centimetre of water to weigh one gramme. In specify- 

 ing quantities of heat we do so in gramme-degrees (Celsius) 

 (gr.°C), or kilogramme-degrees (kg. u C), as the case may be. 

 Similarly, quantities of work are expressed in kilogramme-metres 

 (kgm.). We take the latent heat of one gramme of steam as 

 535 gr.° C, and the specific heat of water as unity, and the 

 mechanical equivalent of heat as - 425 kilogramme-metres per 

 gramme-degree. Therefore the heat required to transform 1*5 grs. 



5—2 



