36 



REPORT 1869. 



between 200 and 500 ft., and the remaining 2° between 500 and 1000 ft. Of the 

 7° -4 less temperature at 1000 ft. high at the first experiment about one-fourth part, 

 or l°-9, took place in the first 100 ft. ; at the last experiment there was no decrease 

 between this space, the temperature being sensibly the same as on the ground up 

 to 200 ft. 



In both states of the sky the temperature at the height of 1000 ft. underwent 

 less change than on the earth, and therefore the rates at which the temperature 

 changes with the height, is not independent of the time of day. The next Table 

 but one (see p. 37) contains the decrease of temperatui-e for every 100 ft. as found 

 from the preceding Tables in every series of expei-iments. 



On July 17th, 23rd, 24th, and 28th more than one series of experiments were 

 taken during the afternoon hom-s, and in every case the changes are smaller at the 

 later than at the earlier experiments. On JiUy 23rd and 24th nine sets of experi- 

 ments were made on each day, between the hours of 3 p.m. and 7.30 p.m. ; ou the 

 foi-mer under a cloudy, and ou the latter under a clear sky. In both series the largest 

 changes are those in the first set of experiments ; and the smallest those in the 

 last set, so that experiments made at the same hours must be grouped together 

 and distinct from those at other times. Comparing the changes in the first 100 ft., 

 it will be seen they are larger with a clear than a with cloudy sky. By comparing 

 the general results with the two states of the sky together, it will be seen that 

 the changes from hoiu: to horn- are less with the cloudy than with the clear sky, 

 and consequently the experiments in the two states of the sky must be treated 

 separately. The following Table has been formed by taking the means of obser- 

 vations between the same hours in the two different states of clear and cloudy skies. 



Table showing the mean decrease of Temperatm-e for every increase of 100 ft. of 

 Height depending on the hour of the day and the state of the sky. 



These numbers were then laid do'RTi on diagrams, the heights as ordinates and 

 the decrease of temperature as abscissa ; these points were joined, and a line 

 was di-awn to pass through or near to them giving equal weight to every point. 



In all these curves there was a decrease of temperature with increase of eleva- 



