OLAISHER'S BALLOON ASCENTS.] 



METEOROLOGY. 



1181 



The preceding extracts, from Mr. Glaisher's de- 

 scription of his aerial voyage, afford our readers a general 

 idea of the scope and objects which the British Associa- 

 tion had in view when they first adopted balloon ascents, 

 for the investigation of meteorological phenomena. 

 Before stating the results which Mr. Glaisher has ob- 

 tained, we may properly call attention to the variety of 

 subjects which might be elucidated by observations 

 carried on at a considerable height from the surface of 

 the earth, and under circumstances in which numerous 

 locally interfering causes would be absent. 



In astronomical observations, it is of the highest im- 

 portance that the proper refraction for any altitude of a 

 star should be ascertained. The nearer the horizon, the 

 greater is the refractive effect of the atmosphere on the 

 apparent position of a heavenly body. Again, the 

 amount of refraction depends not only on the altitude of 

 the body, but also on the varying density of the atmo- 

 sphere, its humidity, temperature, <fcc. Some of the 

 effects of these accidents on terrestrial objects, have been 

 already described in connection with the phenomena of 

 the Mirage, &c. ;* and the consideration of them will 

 point out how essential an accurate estimation of their 

 nature and amount is to the practical astronomer. 



In estimating the force of gravity at any point on the 

 surface of the earth, the pendulum is universally em- 

 ployed ; and according to the number of its vibrations, 

 in a given time, so the intensity of gravitating force is 

 indicated for the place. In a similar manner, the vibra- 

 tions of the magnetic needle may be made a measure of 

 t increase or decrease of magnetic force, at any two 

 altitudes when compared together. This subject is of 

 extreme importance in connection with the philosophy of 

 the Uudulatory Forces, and one to which we have already 

 directed atvention in the Section on Magnetism. Our 

 knowledge of the force of gravitation, may be enlarged 

 by considering the attracting power, or perturbing forces, 

 which each and all of the planets mutually exercise ; 

 whilst with respect to the Maijnetic forces, our investiga- 

 tions are necessarily limited to the phenomena exhibited, 

 on, a little beneath, or a short distance above, the surface 

 of our globe. 



The theoretical constitution of our atmosphere has been 

 determined with comparative precision ; but its actual 

 composition, at various altitudes, must necessarily de- 

 pend on local disturbing causes. It is but reasonable to 

 suppose, tliat the neighbourhood of large towns would 

 present an atmosphere tainted with the impurities pro- 

 duced by manufacturing operations, furnaces, and a 

 crowded population. The fact of the air, in such locali- 

 ties, being deteriorated, has long been familiarly known ; 

 but the amount of impurity dissolved in the air, under 

 such circumstances, and at varying heights, has not been 

 even approximately measured until recently. The pre- 

 sence or absence of ozone, affords us a means of testing 

 the rcspirable qualities of the air, as has been already 

 pointed out at a previous page, t 



In the article on Photography, we explained the pecu- 

 liar effects of the actinic rays of light on salts of silver, 

 Ac. t Now the daily experience of every operator teaches 

 him, that considerable difference in the power of the 

 actinic rays is constantly occurring. A change of atmo- 

 spheric humidity, amount of cloud, etc., is instantly 

 attended with an increase or decrease of actinic force ; 

 and hence the varying time required to take a good 

 photograph, especially in landscape effects. We also find, 

 that within the tropics, at the level of the sea, it is diffi- 

 cult to get a good impression on the sensitive plate in 

 the camera, although, in the game region, excellent views 

 are produced at considerable altitudes. 



Thus, in connection with Astronomy, Magnetism, 

 Chemistry, and Photography, we must perceive, that 

 investigations carried on in the upper strata of our 

 atmosphere, can but result in an accession to our know- 

 ledge ; for, at a height of a few thousand feet, wo are, to 

 a large extent, removed from irregular and accidental 

 disturbing causes, the presence of which vitiate accurate 

 observations and successful experiments in any of the 

 See ante, pp. 1147, 11M. t See ante, p. 11S2. J See alw ante, p. 57- 



branches of science to which we have referred. It will 

 be unnecessary to urge similar considerations on those 

 who have read the previous pages in this section, in con- 

 nection with meteorological phenomena, which are almost 

 invariably produced at heights above 1,000 feet from tho 

 surface of the earth. Clouds, hail, snow, rain, lightning, 

 meteors or aerolites, (fee., all owe their origin to atmo- 

 spheric disturbances, occurring, in many cases, far above 

 the reach of man, if unaided by the balloon. Science has 

 provided us, in this machine, with a means by which, 

 Daedalus-like, we may fly in the air, and, at our leisure, 

 note phenomena of the utmost importance to the exist- 

 ence of our race. The cui-bono inquiry usually enter- 

 tained in reference to most investigations of a purely 

 scientific nature, may be readily answered, in the case of 

 balloon ascents, by remarking, that if, through our 

 present limited knowledge, obtained by observations on 

 the surface of the earth, we have been enabled to fore- 

 warn the mariner of a coming storm, and save him and 

 his vessel from shipwreck, how much more successful 

 may we hope to become, if we venture into those 

 winds, clouds, and storms which he dreads, and investi- 

 gate their causes, connection, <fec. , in their own regions, 

 under circumstances so essentially fitted for our 

 purpose. 



Having thus pointed out the value of balloon ascents, 

 in a scientific and practical point of view, we proceed to 

 give an analysis of the results which Mr. Glaisher has 

 obtained. 



The chief objects which were sought after in the 

 balloon ascents of 1862, were as follows : 



1- The ratio of increase or decrease of the temperature, 

 and the amount of aqueous vapour in the air, at heights 

 within five miles (20,400 feet) above the sea-level, in 

 this country. 



2. To compare the readings of aneroid and mercurial 

 barometers. 



3. To ascertain the electrical state of the atmosphere 

 at various elevations. 



4. To discover the amount of free ozone. 



6. To register the number of vibrations of a magnetic 

 needle at increasing heights. 



6. To find the relation of the temperature of the air 

 and that of the dew-point, at heights corresponding with 

 those of high lands in India, and other places ; and to 

 compare the indications of the dry and wet bulb-ther- 

 mometers with those of Daniell's and llegnault's hy- 

 grometers. 



7. To collect air at different elevations. 



8. To note the height, kind, thickness, density, (fee., 

 of various strata of clouds. 



9. To ascertain the rate and direction of atmospheric 

 currents. 



10. To make observations on the intensity, &c., of 

 sound. 



Besides the above particulars, it was intended to note 

 any phenomena which might casually present them- 

 selves during the progress of the observations indicated 

 above. The usual kind of meteorological instruments 

 were employed each, however, having been specially 

 prepared for the purpose. Owing to occasional accidents, 

 many of them were broken during descents. 



Eight ascents, in all, were made in 1862; viz., three 

 from Wolverhampton, which was chosen as a central 

 position, and because it afforded a good breadth of land, 

 without the danger of a voyage over the sea ; four from 

 the Crystal Palace at Sydenham ; and one from Hendoii, 

 which was, in fact, a re-ascent from the spot at which 

 the voyagers had alighted on the previous evening. The 

 dates of the ascents were all in the svimmer months, 

 being from July 17 to September 8, inclusive. 



The greatest height attained was on September 5, 

 in an ascent from Wolverhampton. This was estimated 

 to bo at least 36,000 feet ; but as Mr. Glaisher became 

 unconscious, owing to the high de^i-oe of atmospheric 

 rarefaction, the precise elevation was undetermined. 

 In the ascent of July 17, a height of 26,177 feet was 

 attained ; and " in the descent, a mass of vapour, 8,000 

 \ See ante, p. 1173. 



