454 PHILOSOPHICAL TRANSACTIONS. [aNNO 1747-8. 



that body with the rubber, or with the receiver, the communication with the 

 common stock being cut off." 



The solution of this gentleman, in relation to this phenomenon, so exactly 

 corresponds with that which I offered very early last spring, that I could not help 

 communicating it. 



In bodies having the power of readily conducting electricity, this seems to de- 

 pend very little on their specific gravity, simply considered: metals for instance, 

 and water, are in a great degree non-electrics, and consequently conduct elec- 

 tricity the best of any substances, that have yet fallen under our notice; whereas 

 the calces of metals, though very dense bodies, and very greatly more so than 

 water, prevent in a great degree the quick propagation of the electrical power. 

 So that a phial coated within and without with ceruse, i. e. the calx of lead, and 

 electrised, did not, on the application as usual of one hand to the external sur- 

 face, and touching the prime conductor with the other, occasion any shock, or 

 make any explosion, more than the simple stroke from the prime conductor. 

 The same observation holds good with regard to red lead, litharge, and lunar 

 caustic or the calx of silver, none of which snap when electrised. For the same 

 reason, filings of iron, which are rusty, i. e. have their surfaces converted into a 

 calx, are much less proper to be put in glasses to make the Leyden experiment, 

 than those that are not; inasmuch as these last cause a much louder explosion 

 than the first. 



Mr. W. procured a glass jar as large as possible, so that the glass might be 

 very thin; the height of which was 22 inches, the periphery 41. This was 

 covered within and without, leaving a margin of an inch at top, with leaf-brass. 

 As much of the internal surface as was covered amounted to 1 129 square inches. 

 But the difficulty he met with in procuring this glass, was sufficiently recompensed 

 by the great increase of the explosion from it, when fully electrised, and discliarged 

 in the same manner as before. The report was vastly louder; all the attendant 

 phenomena greatly exceeded any thing of this kind he was before acquainted with. 

 As the quantity of metal within this jar did not exceed 2 drams, this experiment 

 gives further weight to his opinion in regard to the manner of increasing the 

 effects of the Leyden experiment; and from what the phenomena of that surpris- 

 ing experiment principally proceed; viz. not from the volume of the prime con- 

 ductor, nor from the quantity of non-electrical matter contained in the glass, but 

 from the number of points of nonTelectrical contact both within and without- 

 side of the glass, and from the density of the matter constituting those points. 

 It must be observed that, cseteris paribus, the electrical explosion is greater from 

 hot water included in glasses, than from cold; and fi-om these glass jars warmed, 

 than when they are cold. 



The explosions from the large glasses just mentioned fully electrised, as well 



