FREE ELECTRICITY.] 



METEOROLOGY. 



1179 



. 



electricity as the cause of those phenomena. It is, how- 

 ever, just as possible that snow and bail may be the 

 cause of the electrical development ; for we may satisfac- 

 torily and independently account for them as arising 

 from the loss of heat and moisture which damp air 

 would sustain in such elevated regions, where the capa- 

 city of the atmosphere for heat is so much greater than 

 near the sea-level. The moisture would be suddenly 

 frozen into hail or snow ; and the rapid transition, and 

 loss of heat, thereby occasioned, may be supposed to be 

 attended with a disturbance of the electric equilibrium, 

 as can be readily demonstrated to occur by experiments 

 on the small scale, conducted on similar principles. 



Numerous attempts have been made to collect free at- 

 mospheric electricity, developed during storms, <fec. ; and 

 perhaps the most successful have been those of Mr. 

 Crosse, to which we have alluded in the Section on Elec- 

 tricity.* On the small scale, this is constantly done by the 

 electrometer used at observatories, but the amount thus 

 collected is insignificant, and not more than sufficient to 

 affect pith-balls or gold leaves. An electric kitet may be 

 employed : it has, however, the disadvantage of incon- 

 stancy of flight, and may be productive of danger to, if 

 not the cause of the death of, the operator. We have 

 often purposed to employ a small silken balloon, well var- 

 nished, and attached to a hempen string, enclosing a thin 

 metallic wire to act as a conductor. This string should 

 run through the balloon, and terminate at the top with 

 a bunch of metallic points. Such an apparatus, if filled 

 with hydrogen,! and properly ballasted, so as to ascend 

 vertically, might be arranged, for the purpose of observa- 

 tion, in a similar manner to that we have suggested for the 

 electric kite, and almost any degree of elevation might 

 be attained; whilst the operator could pursue bis experi- 

 ments safely on the electricity as conducted to him by 

 the metallic thread. We but suggest such an arrange- 

 ment, having never tried it ; yet we believe, with a little 

 precaution, it might be usefully employed. Of course, 

 there would be no chance of the hydrogen igniting, and 

 thus putting an end to the experiment, because the con- 

 ducting wire would pass in unbroken continuity through 

 the balloon, to the apparatus below : the only annoyance 

 would be that of strong winds blowing away the balloon ; 

 this, however, might easily be provided against. Such an 

 experiment should be conducted in a large field, free 

 from trees, and the balloon should be left aloft until 

 every sign of dangerous cloud, mist, <tc. , had disappeared. 

 For experiments on the presence of electricity, when ex- 

 pected in but small quantities at moderate elevations, a 

 fine wire, or string with a fine copper wire inclosed in it, 

 may be attached to an arrow, whilst the other end is in 

 contact with an electroscope. If the arrow be then shot 

 from a bow, as it ascends, the gold leaves or pith-balls will 

 diverge, more or less rapidly, in proportion to the amount 

 of free electricity present. A metallic ball, if connected 

 with the string, and thrown upwards by the hand, may 

 be used instead of the arrow, and is often a convenient 

 arrangement. 



With respect to the cause of free atmospheric elec- 

 tricity, many theories have been proposed ; but the ques- 

 tion is still involved in much obscurity. The air is, 

 perhaps, never absolutely destitute of its presence ; hence 

 this constant evidence of ita existence must be connected 

 with a chain of causes, equally constant in their action. 

 If we inquire into these, we must depend chiefly for ex- 

 planation on the variable quantities of atmospheric 

 moisture, change of temperature, and friction of masses 

 of air in motion. There seem, however, no exactindica- 

 tions afforded as to when we may expect a redundant or 

 deficient state of electrical action. Thus, in winter time, 

 it is well known that free positive electricity is most 

 abundantly noticed, especially during cold, dry, N.E. 

 winds ; and yet, during the moist and hot periods of 

 summer, we observe the most extraordinary instances of 

 electrical disturbance as in the thunder-storms, which 

 I attain their maximum effects in the hot regions of our 

 ; globe. These facts, at first sight, present many difficul- 

 ties. It must be remembered, however, that although 

 See ante, p. 183. + Ibid. * Bee ante, p. 320. 



the surface of our earth may be heated and moist, as in 

 summer, there is always over us, at certain elevations, 

 strata of air, of a temperature far below freezing point 

 perfectly dry, and, therefore, most probably surcharged 

 with free electricity. As we progress from summer to 

 winter, or from low to high latitudes, the intervening 

 stratum of hot and moist air gets thinner and thinner, 

 until the region of perpetual snow and free electricity 

 becomes on a level equal to that of the sea. Now, in 

 summer time, the earth, hot air, and superincumbent 

 cold air, present an analogous case to that of the Leyden 

 jar, which we have already explained ; whilst in winter, 

 the intervening hot air is absent, and the conditions just 

 named are also wanting. From these facts we may thus 

 see how it is that thunder-storms are most prevalent in 

 hot weather ; and, at the same time, why free electricity 

 may be more readily noticed in winter than in summer ; 

 the former (or winter) involving a question of conduction, 

 and the latter of induction, in respect to the laws of elec- 

 trical science. 



In assigning any probable cause of the constant pre- 

 sence of free electricity, we are in the predicament of not 

 being able to reproduce on the small scale, in our labora- 

 tories, the same circumstances as transpire on the large 

 scale in nature. Nothing is easier than to afford free 

 electricity by the friction of glass, or other solid bodies ; 

 but to perform the same operation on either dry or 

 moist air, so as to be able to draw intelligible and deci- 

 sive inferences, has yet to be accomplished. By analogy, 

 we may suppose that two currents of air passing parallel, 

 either horizontally or vertically, and in opposite direc- 

 tions or together, at unequal velocities, may, by their 

 friction, like that of silk and glass, || develop free electri- 

 city : or again, that the difference of heat between two 

 currents, in impact or parallel contact, may produce it 

 in a manner similar to that of the Thermo-electric bat- 

 tery, fl Separately, or conjointly, both these causes may 

 be called into operation ; for we frequently notice, during 

 a thunder-storm, that the clouds move in contrary direc- 

 tions, indicating the existence of opposed air-currents, 

 whilst, at the same time, we find that extremes of tem- 

 perature simultaneously exist, as shown by the hail- 

 shower in the midst of the hottest summer day. 



As meteorological science becomes better known, and 

 more extensively cultivated, we may hope for the 

 establishment of observatories, where tho electrical state 

 of the atmosphere at different heights, at the same timo 

 and place, may be observed and registered, after the 

 manner that is now adopted with the barometer and 

 thermometer. We shall then have another and most 

 important element added, in enabling us to study atmo- 

 spheric conditions now involved in obscurity ; and perhaps 

 may succeed in unravelling the connection which subsists 

 between them. 



ME. GLAISHER'S BALLOON ASCENTS, ETC. 



If our atmosphere were ever at rest, and unaffected by 

 heat, moisture, &c. ; or, in other words, were it merely 

 a mixture of the two gases, oxygen and nitrogen, and 

 solely acted on by the laws of gravitation, then its den- 

 sity would gradually diminish upwards, its capacity for 

 heat .would increase, and the sensible temperature fall. 

 To ascertain how far these laws are disturbed by the 

 abnormal conditions into which the lower mass of our 

 atmosphere is thrown, becomes, therefore, a matter of 

 deep scientific interest. 



Some time ago, the British Association voted a sum 

 for the purpose of defraying the expense of balloon 

 ascents, by which meteorological observations, at various 

 heights above the surface of the earth, might be carried 

 on. We need scarcely remind our readers that no other 

 mode exists of carrying out such observations, except 

 that of ascending high mountains ; and, in this way, tho 

 difficulties met with, and the inconvenience to which the 

 observer is subjected, are alin9st insuperable. No such 

 objection can arise when balloons are employed. In the 

 course of a few minutes after leaving the earth, the 

 I See ante, p. 183. || See ante, p. 170. H See ante, p. 241. 



