294 M. De la Rive on the Formation of Hail. 



rolling murmuring which is perceived at so great a distance, is 

 owing to the combination of the individual sounds produced by 

 each hailstone cutting the air with such swiftness. The clashing 

 of any hailstones during their progress causes them immediately 

 to descend. 



Qth, We are led to suppose that the hailstones are subjected 

 to a rapid rotatory motion, but my opportunities have not yet 

 enabled me distinctly to see it. 



1th, The formation of hailstones, and their increase, appears 

 owing to cold produced by the evaporation at their surface, 

 on account of their great velocity. The hot air into which the 

 anterior edge of the cloud penetrates, leaves a portion of water 

 deposited upon them, a part of which is evaporated, and thereby 

 congeals the other part, and thus forms concentric layers round 

 the nucleus ; the wind unceasingly transports the hailstones into 

 new portions of air which is saturated with moisture, and the 

 upper cloud supports them in their progress. But the lower 

 cloud rapidly increasing in density by degrees falls down, and 

 separates itself, more especially on its anterior portion, from the 

 electrical cloud which supports it, till it reaches that'point in which 

 the action of this latter^is almost nothing, the hailstones being all 

 electrified in the same manner then strongly repel each other, 

 and present that violent agitation which is perceived at the surface 

 of the earth, and which repels in all directions those hailstones 

 which the wind reunites by imposing upon them its own direc- 

 tion. 



Sth, The presence of long crystals at the opposite poles of the 

 hailstones of the 28th of July 1835, would indicate that those 

 which were placed at the equator were destroyed during their 

 descent by the^rotatory motion, or that this same movement 

 hindered them from being formed upon the equatorial portion 

 on account of their velocity, whilst they were easily grouped 

 upon the poles. 



^th^ The water procured from the melting of the hailstones 

 was far from being pure. 



From this short review, we may see how necessary it is, es- 

 pecially in meteorology, to guard against too readily generalising 

 facts. We must first observe, and then observe again, and we 



