264 *^N THE ELECTRIC COLUMN, 



with tlie latter this analogy of cause, that they are explosions 

 of a. iparUcular exjmnsiblejirdd, procluced by that kind of 

 sudden decomposition of atmospheric air, as it happens by 

 fjiing gunpowder and other processes. 

 Hail, yil. A direct proof of these sudden decompositions of 



some substances in such clouds, and simultaneous composi- 

 tions of other substances, is the production of hail. This 

 effect shows, that, in a certain combination of circumstances, 

 such a quantity of free fire enters suddenly into some com- 

 bination, that \\\c freezing point is much surpassed in the 

 upper part of the clouds : hence the formation of grains of 

 Sleet. sleet so cold, that in falling through the clouds, their size is 



increased in the form of icicles, by the watery vesiculse 

 freezing upon them ; of which formation the hail-stones bear 

 all the characters, especially by having in the centre that 

 opaque grain of 5/c'f/. 

 Other phono- The foregoing are the most conspicuous of the operations 

 bl'^^n rh '*'^?^' produced, at certam times, in some strata of the atnaosphere, 

 4iiosphere. > but not all those which an attentive observer may perceive : 

 they are here, as must be the case in the first steps con- 

 cerning all invisible processes producing visible effects, ex- 

 j)lained ©nly by g-ewera/ analogies with known causes in our 

 chemical processes; and if we cannot yet approach nearer 

 to specific causes, it is because we are still very backward 

 in the knowledge of the subtile fiuids, which, at different 

 times, come to mix with air in the atmosphere. We cannot 

 however dcubt, that to such fivids is owing the multitude 

 pf phenomena still unexplained intelligibly, both in the 

 atmosphere itself, and in its connexions with vegetation and 

 the animal economy, when we consider what progress has 

 been made in this knowledge, by only attending to the che- 

 viical affinities of light and fire, and by a beginning of dis- 

 covery on those of electric fiuid, the existence of which on 

 bodies would be unknown to us, were it not for the motions 

 produced in visible bodies, by the disturbance of its equi- 

 librium : this is one of its characteristic properties, and our 

 test of the degrees of its intensity in different cases; as the 

 thermometer is for firee fire, and vision for light. 

 Tests of the These first steps in the knowledge of causes, which are 



«ptual state of thcmsi:\\ Qi imperceptible, must render experimental philo- 

 sophers 



