EXPERIMENTS WITH BALLOONS. 57 



for the purposes just indicated, the observations of the thermometer and 

 dew-point should, if possible, be unremitted during the whole time both of 

 the ascent and descent, and, of course, must be accompanied by simultaneous 

 observations of the barometer : one person's time should therefore be wholly 

 devoted to these objects ; and the arrangement should be well considered, by 

 which his labour may be facilitated and his attention kept undistracted. The 

 prevailing forms and structure of the clouds ; their internal motions, if any ; 

 the number of strata which may be detected, and the number and direction 

 of the currents which their motion may indicate, will also form interesting 

 objects of observation in conjunction with the preceding. Contemporaneous 

 observations will, of course, be made on the earth during the time of the 

 aerostatic voyage, which will possess a greatly-increased interest if circum- 

 stances should permit it to take place on the day when hourly meteorological 

 observations are made at all the principal observatories of Europe, according 

 to the plan laid down by Sir J. Herschel. Portions of the air should be 

 brought down, for examination, from the highest elevations ; and this may 

 probably be best effected by taking up several glass balloons, or bottles care- 

 fully gauged, fitted with stop-cocks, and filled with water. The water should 

 be allowed to run out at the proper station, and the stop-cocks closed. Ex- 

 periments upon the radiation of heat, by another observer, would also be 

 interesting, although there are probably no knpwn means of instituting them 

 with all the accuracy which could be desired. Observations with Sir J. Her- 

 schel's actinometer might be made upon the force of solar radiation at various 

 heights ; but the instrument would not be applicable to the measurement of 

 terrestrial radiation. When a delicate thermometer, whose bulb is covered 

 with lamp-black, is placed in the focus of a parabolic reflector, and turned 

 towards the clear sky, even in the day-time, it will radiate a portion of its 

 heat into space ; by the same contrivance, the rays of heat proceeding from 

 the earth, or from beds of clouds, would be condensed upon the thermometer, 

 and some estimate formed of their intensity. Observations upon these points 

 at different heights, and at different periods of the day and night, would be 

 instructive, though not of the high importance which would belong to those 

 of the thermometer and hygrometei*. To these observations might be added 

 others of great interest upon the electricity of the atmosphere, by dropping 

 wires into clouds, or from stratum to stratum of cloudless air, and examining 

 the nature of the electricity of their extremity by means of a very delicate 

 electroscope : but attractive as these researches may prove, the Committee 

 recommend, that should a series of ascents be undertaken by one or many 

 observers, on no occasion should the observer's attention be distracted by too 

 great a variety of objects ; and that our efforts should at first be directed 

 solely to the elucidation of the question of the decrease of temperature, by 

 the acquisition of accurate contemporaneous observations of the barometer 

 and thermometer made at different elevations. It would manifestly be 

 desirable, that Avhile observations of atmospheric temperature and pressure 

 were made in a balloon, two observers, stationed at the extremities of an 

 accurately measured base, and provided with theodolites of the best con- 

 struction, should by their observations determine the height of the balloon 

 geometrically, at the instants the observations of tempei'ature and pressure 

 were made. This, however, implies a more extensive system of cooperation, 

 and a larger personal and instrumental force, than could probably be assem- 

 bled. It will, therefore, be best to confine the observations simply to the 

 determination of corresponding teiuperatures and pressures of the atmo- 

 sphere. For this purpose nothing more is wanted than a supply of instru- 

 ments that can be easily used and give accurate results. 



