Solar Radiation 



391 



The main results of Vallot's observations are as follows. 

 The ratio between the heat received in the same time by 

 the same area exposed perpendicularly to the sun's rays on 

 Mont Blanc and at Chamonix was found to be 0*82 to 0*85, 

 which agreed well with the proportion found by Violle in 

 1875. The value of the solar radiation found was, however, 

 much lower than that found by Violle. The maximum 

 values observed by Vallot were 1*56 gr. C. on Mont Blanc 

 and 1*33 gr. C. at Chamonix, whilst Violle found 2^39 gr. C. 

 on Mont Blanc and 2*01 gr. C. at the Glacier des Bossons 

 in the valley. Violle's observed values are therefore half as 

 great again as Vallot's. No explanation of the cause of this 

 discrepancy is offered, but it is pointed out that the values 

 observed by Crova at Montpelier are more in accordance 

 with Vallot's than with Violle's. They are interesting in 

 themselves and are worth quoting. They relate to the year 

 1895, the summer of which was very hot. 



Intensity of solar radiation observed by M. Crova at Mont- 

 pelier in 1895, in gramme-degrees per square centimetre 

 per minute. 



The subject was taken up again by Vallot in 1891, and 

 this time he used the mercury actinometer of Crova (Ann. 

 Chim. Phys. 1877 [5], xi. 461). 



The result of the experiments in 1891 was in the main 

 confirmatory of those obtained in 1887. In the following 

 table the intensities of solar radiation on September 19, 1891, 

 are given as observed on Mont Blanc and at Chamonix : . 



