Prince Rupert's Drop, or Glass Tear. 337 



ciium." And although I will not take upon me to justify 

 all their decisions, or even this dogma itself upon their 

 prineiple; yet as this secnis the na plus ultra of human 

 means to procure one, and w I)ich, after all, appears not to 

 be abioliitcly so, 1 think their assertion is not remote 

 enough from truth to justify a rash contradiction on our 

 part,"or to arraign the profundity of their knowledge. But 

 to return : How great must be the velocity, how great 

 the mechanical collision, to rend asunder with sucli force 

 so well compacted a substance as the glass of which these 

 granades are made, even after ir.aking every reasonable 

 allowance for its want of annealing, which no doubt in- 

 creases its fragility, while it hardens the suiface ! There 

 must be something more than mere mechanical influx, or 

 consequent collision, to rend asunder and reduce to powder 

 an impregnable mass, which is capable of n-sistmg the 

 weight or many tons, sustaining the force of a large vice, 

 or the rude strokes of a hammer (after allowing for the 

 geometric resistance on the external attack, and the want of 

 the san)e in the internal force) used in breaking them, be- 

 fore this phenomenon will be satisfactorily explained. 



And without giving a more elaborate definition than the 

 thing is obviously susecptilde of, f conceive this cau=e to he 

 electricity : and that, in the formation of the drop, after the 

 caloric particles have pervaded the glass and subsided, this 

 matter, like a iamhentjame, attaches to and lines the inte- 

 rior surface or cavities, as in the Leyden jar; and by tliis 

 hermetic accident (for it is not properly art) niay remain 

 prisoner for many centuries ; but yet, though pent up, (being 

 perfectly insulated) is not diminished : therefore, upon 

 opening [\\c conduit pipe of connnunieation in the tail, the 

 affir.ity the inclosed effluvium has w ith that in the air, our 

 hands, or whatever else breaks them, Causes that violent de^- 

 tonation,and thedestruclion thereof considered there\\ ith to 

 take place, and the force of llie explosion is (ctF-ieih pariliis) 

 in a compound, direct, ratio with the capacity of ihc cavi- 

 ties, and the sttcnuth of materials. 



'J'hus Is is, when a vaciumi is induced of necessity, and 

 of materials which, while they are extremely friable on tlie 

 one hand,, arc impervious to both influx and efflux on the 

 other 3 (hence the want of tlase appearances in breaking 

 steel, &:c.) and void of «M.rv other occupant than iliis 

 clastic vapour, which is g, tier.ucd in their first formation, 

 which, like seed in the wcaub, seems to- be the very gern; nr 

 rudimenl of elementary fire, and oniv \\all.i the iiiviiation 

 of excitation to manifest itself: and svhenever this ^xcita- 

 Y 3 tion 



