24 



Mr. J. Tyndall. 



[Feb. 8, 



6.30 p.m Air 36° Wool 31° 



7 „ „ 36 „ 28 



28 



7'30 ,, 35^- 



8 „ 35 



8.30 „ „ 34 



9 „ „ .35 



10 „ „ 35 



10.30 „ „ 35 



26 

 25 

 27 

 28 

 29 



After this last observation, my notes contain the remark, "Atmo- 

 sphere exquisitely clear. From zenith to horizon cloudless all round." 



Here, again, the difference of 4° between the temperature of the 

 wool at 8.30 p.m., and its temperature at 10.30 p.m., is not to be 

 referred to any sensible change in the condition of the atmosphere. 



The observations were continued on January 17th, 23rd, 24th, 25th, 

 and 30th ; but I will confine myself to the results obtained on the 

 evening of the day last mentioned. The thermometers were ex- 

 posed at 6.45 p.m., and by aid of a lamp read off from time to time 

 afterwards. 



7.15 p.m Air 32° Wool 26° 



8 „ „ 31 „ 26 



9.30 „ „ 31 „ 27 



During these observations the atmosphere was very serene. There 

 was no moon, but the firmament was powdered with stars. The 

 serenity, however, had been preceded by heavy rain, which doubtless 

 had left the atmosphere charged with aqueous vapour. The movement 

 of the air was from the south-west and light. Here again, with an 

 atmosphere at least as clear as that on December 10th, the difference 

 between air and wool did not amount to one-fourth of that observed 

 on the latter occasion. 



The results obtained on February 3rd were corroborative. The 

 thermometers were exposed at 6.15 p.m. 



7.15 p.m Air 34° Wool 28° 



8.25 „ „ 34 „ 30 



Here again, the difference between air and wool is only 4 degrees, 

 although the sky was cloudless, and the stars were bright. The 

 movement of the air was from the south-west and light. 



On the forenoon of this day there had been a heavy and persistent 

 rain storm. Heavy rain and high wind also occurred on the night 

 following. The serene interval during which the observations were 

 made lay, therefore, between the two storms. Doubtless the gap was 

 well filled with pure aqueous vapour. 



Further observations were made in considerable numbers, but they 



