392 



Solar Radiation 



The mean value of the ratio of the intensities is o - 84, as 

 before. The values of the intensity of radiation are rather 

 lower than those found in 1887. 



In the year 1896 Prof. Angstrom, of Upsala, made 

 observations on the peak of Tenerife with a special form 

 of actinometer depending on the heating of metal plates. 

 He made observations at three different elevations, namely, 

 at Guimar, 360 metres, Canada, 2125 metres, and at the 

 summit, 3683 metres. Reduced to a uniform thickness of 

 one atmosphere corresponding to a pressure of 760 mm., the 

 intensity of radiation by the vertical sun was found to be at 

 Guimar 1-39, at Canada 1*51, and at the summit 1*54 gramme- 

 degrees per square centimetre per minute. These values 

 agree more closely with the values found in 1887 by Vallot 

 than with those of 1891. But the values found by Crova, 

 Vallot and Angstrom are all of the same order. 



The writer's observations with the steam calorimeter in 

 Egypt in May 1882 were undertaken with the object of 

 ascertaining the maximum rate of distillation near the sea- 

 level under the most favourable circumstances. This occurred 

 during the forenoon of May 18, when the meteorological con- 

 ditions were as favourable as they could be. The sun shone 

 steadily in a cloudless sky and the air was motionless. The 

 shade temperature reached 4O'5 C. in the course of the day. 

 Time was taken as portions of 5 cubic centimetres were 

 distilled. The shortest time in which this quantity passed 

 was 3 m. 20 s. This is at the rate of 1-5 c.c. per minute, 

 and it occurred twice in the forenoon, namely at 10 h. 37 m. 



