Mr. J. P. Harrison on Radiation and Vapour. 285 



1. If the sun was iti even moderately high altitude, the rays 

 could not reach the instruments. 



2. Most of the ascents took place early or late in the day, 

 when the sun was in very low elevation ; or if nearer midday, 

 at seasons when from its altitude the sun has also little power. 



3. A balloon is constantly "gyrating;" so that the instru- 

 ments were more frequently in the shade of the several persons 

 who occupied the car than in sunshine; in addition to which 

 there were shadows. from the numerous ropes. 



4. Under these circumstances, even when moved into the sun, 

 the few seconds allowed for taking observations with the solar 

 thermometer would not suffice for heat to be absorbed and con- 

 ducted through the mercury. 



5. The solar thermometer was not placed in a box so as to be 

 protected from the wind. 



6. And the delicate blackened-bulb thermometer, which is 

 most frequently alluded to, does not appear to have been enclosed 

 in a glass sphere. 



That the cause of the slight differences between the readings 

 of the shaded and exposed thermometers must be sought for 

 within the car of the balloon itself and the circumstances at- 

 tending the several ascents, would further appear to be evident 

 from the fact that the readings of the solar thermometer ob- 

 tained under half a mile (2640 feet) above the sea-level also differ 

 very little from those which were taken in shade. The parti- 

 culars of each case, which are exhibited in the following Table, 

 are extracted from the several reports which were presented to 

 the British Association in 1864 and 1865*. 



Table of Thermometric Observations taken during Mr. Glaisher's 

 balloon ascents. • 









Thermometers. 





Dat~. 



Hour. 



Height. 



Dry- 



bulb. 



Wet- 

 bulb. 



Delicate 

 black- 

 bulb. 



Remarks. 





h m s 



feet. 











Feb. 27, 1865. 



1 59 p.m. 



474 



49-5 F. 



420 F. 



51-5 F. 





Dec. 1, 1864. 



2 39 „ 



890 



472 



43-3 



47-0 



Sun shining brightly. 



June 27, 1864. 



7 4 0,, 



1578 



540 



47-8 



53-5 



Sun at edge of cloud. 



Dec. 1, 1864. 



2 41 „ 



1618 



450 



41 2 



44-5 



Sun shining brightly. 



Aug. 29, 1864. 



4 8 30 „ 



1883 



68-2 



55-5 



70 





Aug. 31, 1863. 



6 15 40 „ 



1963 



51-5 



490 



520 



Sun shining. 



| Sept. 29, 1863. 



10 19 a.m. 



2039 



470 



375 



530 





! June 13, 1864. 



7 11 30 p.m. 



2380 



52-8 



45-9 



55-5 



Sun bright. 



* No observations of black-bulb thermometers were published in 13G2 

 and 1863. 



