33 S Expcrbnenis on the Hand Granade, &c. 



tion is begun, how irresistible are (he effects produced by 

 it! I believe nothing in nature ('f small things might be 

 compared with great) is more analogous to an earthquake 

 than the bursting of one of these little tears of glass, or 

 more like it in its cause ; for both arise from a sudden 

 combustion of a latent and inflanmiable principle contained 

 in their interior parts ; and both alike cause a derangement 

 of the parts which heretofore formed their orbicular prisons. 

 To ascertain whethei they were charged ^/?/s' or minj/s*,! 

 placed them in an insulated situation, on a large flint glass 

 condensing receiver; and with a hammer of the same kind 

 of glass (both being well excited) I broke some of them at 

 the small end : but, contrary to my expectation, the result 

 was the same as if broken in my hand. 



I next placed some of them on a table, which I knew to 

 be a good conductor, and with mv glass mallet or hannner 

 I broke several more with precisely the satpe effect. 



I also broke some with a conducting, i. e. a cornmon 

 hammer, upon the excited receiver, but there was no diffe^ 

 rence in the effect : for all the means I made use of (how- 

 ever varied) were productive of the same appearances as 

 when broken in my band, or by the collision of a conduct- 

 ing substance, while they were placed upon another con- 

 ductor. 



And now, having varied the experiment by all the means 

 I could devise, except I had tried the air-pump, (which I 

 could not do, as 1 had not got an open receiver,) ] began to 

 doubt whether electricity had any share in this phaenome-: 

 non or not, and to conclude the effect must be purely me- 

 chanical (for I would not call it a Ivms iintiircp) ; when 

 what compensated all my trouble, and put the matter past 

 doubt, was this : 



I darkened the room entirely, having previously furnished 

 myself with a clear strong glass receiver to prevent the ac- 

 cident of the pieces flying into mv eyes ; then directing 

 these organs of vision bv the feel, 1 broke several in this in- 

 closure, where they uniformly produced a bright corrusca- 

 tion like lightning; which, together with the more than 

 mechanical snap they make upon breaking, quite satisfied 



* To those who are iinacqu.iinted with the history of electricity, it may 

 be needful tn observe, that the terms plus and Tin}iu<:, + — ; posiiive and 

 negative; vitreous and resinous; are not six different electrical qualities; 

 but three sets of equivalent terms, in diti'trent systems of the same science, 

 indicative of the two or contrary principles which reciprocally atlract each 

 other, and cause what is called the clirlrii sliock. There are also other 

 terms by way of desigfnating the sarac principles, as terrene and atmofpheiic ; 

 but these are not so common. 



nie 



