TRANSACTIONS OF THE SECTIONS. 37 



On the Changes of Temperature and Hmniditij of the Air tip to XOOQ feet, from 

 ohservations made in the Car of M. GiffanVs Captive Balloon, By Jajies 

 Glaisher, F.R.S., F.B.A.S., cjr. 



[A communication ordered to be printed in extenso in the Proceedings.] 



The necessity which existed in all the free balloon ascents I made in connexion 

 with the British Association of leaving the earth with a great ascending power 

 to avoid striking adjacent buildings, caused the first few hundred feet to be passed 

 through too quickly to enable me to determine satisfactorily the temperature and 

 humidity of the air at the lower elevations ; at the higher elevations the obser- 

 vations Avere repeated at vnW, as I could descend by allowing an escape of gas, 

 or ascend by discharging sand as frequently as I thought desirable. The Avant of 

 the power of repetition of observation within 1000 feet of the earth has caused 

 our knowledge of the temperature and humidity of the air within this distance to 

 be more limited and less accurate than at higher elevations. The theory of the 

 decline of P of temperature in every increase of 300 ft. of elevation was proved to be 

 erroneoii? in everv ascent; in some a decrease of 1° and more than 1° was experi- 

 enced within the first 100 ft. (see ascents, July 30th, Eeport 18(32; July 11th, 

 Report 1863 ; and August 31st, Report 1863 and 1864), notwithstanding the 

 rapidity of motion ; and there is no doubt that if the balloon could have been kept 

 stationary at the height of 100 ft. on those occasions the decline would have been 

 much greater, whilst in others there has been no decrease of temperature within 

 this space (see April 6th, Report 1864 ; and Dec. 1st, 1864, Report 1865). 



In some of the ascents a decline of 8° or 10' was met with within 1000 ft. of 

 the earth (see ascents of July 30th, 1862 ; August 18th, 1862 ; July 11th, 1863 ; 

 August 31st, 1863, &c.), whilst in others but little or no difference was found 

 within 1000 ft. of the earth. This was very remarkably shoAvn in the descent on 

 June 13th, 1864, which was made at about sunset ; after this ascent it was noticed 

 that whenever ascents had been made in the afternoon hours the changes of tem- 

 perature near the earth were smaller at the time of descent than at the time of 

 ascent ; but this was not found to be the case with the ascents which had been 

 made in the morning hours. Two ascents only were made after sunset, the one on 

 October 2nd, 18(35, with a clear sky, and the other on December 2nd, 1865, -nath a 

 cloudy sky ; in the former, with a clear sky, the temperature increased on leaving 

 the earth, and continued to increase with elevation, began to decrease on descending 

 and continued to decrease till the earth was reached, the change of temperature 

 during the ascent being somewhat smaller than during the descent. The second 

 night-ascent on December 2ud, 1865, was made with a cloudy sky ; the tempe- 

 rature at first decreased, then became stationary, then increased when between 1400 

 and 1800 ft. liigh ; at greater heights the temperature decreased ; thus towards the 

 end of the series of experiments, which were made for the British Association, it 

 was found that the observations indicated that the change of temperature near the 

 earth varied greatly, followed no constant law, in fact, appearing to differ at the 

 different hours of the day ; but the ascents were too few in number and too dis- 

 connected (having been made in every month of the year, at different times of the 

 da)' and under different states of the sky) to be able to say positively that such was 

 the case. 



These experiments, however, unsettled our previous views, and caused a suspi- 

 cion to rest on the amounts applied for correction of refraction in astronomical 

 observations. 



The great captive balloon, recently located at Ashburnham Park, Chelsea, and 

 Icept constantly inflated with 420,000 cubic feet of hydrogen gas, in connexion 

 with a powerful steam-engine, was admirably adapted to settle all these points, 

 and M. Gitfard, its proprietor, most kindly placed it at my disposal for any series 

 of experiments to which I could apply it. 



This balloon could ascend on a calm day to the height of 2000 ft. ; its rate of 

 ascension could be regulated, and the ballooa could be kept all but stationary at 

 any point, for anj' length of time. 



