Observations made with a Black Bulb Thermometer.. 83 



rature 10 o, 6 above, and a temperature-difference 3°'6 above the 

 annual means when the monthly mean humidity is lowest ; and 

 the lowest mean maximum, and nearly the lowest temperature- 

 difference with almost the highest relative humidity .* 



It seems necessary, then, to compare the various elements in 

 some more effective way. First of all, to show the tendency of 

 a variation in the cloudiness of the sky, Table III. has been con- 

 structed. It gives for each percentage of cloud — 



(1) The number of observations ; 



(2) The annual mean maximum temperatures in the sun and 

 shade, and the difference of maxima ; 



(3) The annual mean values of the dew-point and relative humidity 

 at noon. 



The mark ... signifies that the sky is cloudless, per cent, that 

 there is some cloud but less in quantity than 5 per cent, of the whole 

 sky. In a great number of instances this last includes clouds lying 

 low down on the horizon. 



TABLE III. 



The Elements arranged in a Sequence of Cloud 



Percentages. 



Cloud %. 



No. of 

 Observa- 

 tions. 



Annual 



Mean 



Dew-point 



at Noon. 



Annual 



Mean 



Relative 



Humidity 



at Noon. 



Annual 



Mean 



Maxima in 



the Sun. 



Annual 

 Mean 



Maxima 

 in the 

 Shade. 



Annual 

 Difference 



of 

 Maxima. 





424 



o 



40 



% 

 30 







136 







79 







57 







114 



42 



31 



138 



81 



57 



10 



119 



44 



34 



137 



80 



57 



20 



117 



44 



34 



138 



79 



59 



30 



119 



45 



34 



140 



82 



58 



40 



110 



46 



36 



141 



80 



61 



50 



105 



45 



35 



142 



80 



62 



60 



100 



46 



39 



141 



79 



62 



70 



78 



47 



41 



139 



77 



62 



80 



77 



47 



41 



139 



77 



62 



90 



46 



49 



52 



132 



76 



56 



100 



51 



50 



61 



113 



69 



54 



We see from this Table that on the whole the temperature of the 

 dew-point, and the relative humidity, both increase with the increase 

 of cloud. The temperature in the sun, however, is at its highest 



* E. T. Smith could not find any directly traceable connection between aqueous 

 vapour tension and solar radiation. But he only discussed monthly averages. 

 See Q. J. R. Met. S., July, 1886, p. 188. 



