284 



Intensity of Rays of High Ref Tangibility . 



rain, &c 



The bulbs were tested, when filled with dry air, by 

 exposing them to intense sunlight : it was found that, although 

 the temperature within the shade varied from 15° to 40° C., 

 the compensation was so complete that practically no deviation 

 from the straight line, described by the pen on the drum, 

 was observed ; the bulbs were fixed to the beam (as nearly as 

 possible over the point of support) by means of cylinders of 

 thin sheet-brass, which were slipped over the acid tubes and 

 screwed to the beam. The instrument was calibrated by 

 means of the silver-chloride actinometer. The result of six 

 series of observations gave the following values in intensity 

 units corresponding to one division on the curve-paper : — 



1 series mean of 11 observations *021 



2 



?? 



» 



14 „ 



•029 



3 



?? 



?? 



10 „ 



•043 



4 



n 



j? 



15 „ 



•025 



5 



» 



>? 



9 



•033 



6 



j? 



>? 



10 „ 



•029 



Mean = -030 

 In the following table the observation from one of the 



series is given . 



— 







Intensity 

 (unit = 1). 



Value of 

 1 division in 



light units. 



Eecalculated 



intensity from 



curre. 



Time of day in 

 hours. 



0-3758 

 0-1022 

 0-1693 

 0-3240 

 0-3348 

 0-3210 

 0-4457 

 0-0779 

 0-1087 



0-0385 



0-0328 



0-027 



0-035 



0-029 



0-030 



0039 



0-017 



0021 



0-2925 

 0-1275 

 0-1875 

 0-2475 

 0-3375 

 0-3150 

 0-3375 

 0-1350 

 0-1500 



10-75 



10-8 



11-0 



11-08 



11-5 



11-6 



11-65 



12-3 



12-6 



The curve from which the data are obtained is shown in 

 fig. 1, Plate IV., the value of one division being equal to -fo 

 of a square therein represented. 



In fig. 2, Plate IV., the results obtained above are mul- 

 tiplied by 100 and represented graphically. Fig. 3 repre- 

 sents the curves registered by the recording apparatus under 

 varying conditions of light from June 13 to 16. It will be 

 seen that such an instrument as this will record continuously 

 the actinic intensity of the light under all conditions of 

 weather throughout the year, and requires no attention 

 further than winding the clock whereby the motion of the 

 drum is maintained. 



