VOL. H.J PHILOSOPHICAL TRANSACTIOXS. 335 



wards dried, but most clearly because the finest filings or powders of metals 

 conduct as readily as the entire substances do. 



But though this change will not succeed in metallic substances on mere pulveri- 

 zation, yet it seems to follow in most other hard bodies. Having dried a 

 piece of Portland stone, he found it conducted perfectly well ; but on powder- 

 ing, and sealing it up in one of the tubes with the wire ends, as above, it be- 

 came a perfect resister, or non-conductor, like the metallic calces. He tried 

 the same experiment on a variety of other bodies, particularly gum arable and 

 alum ; and had reason to believe it will succeed in all bodies that can be pulve- 

 rized in the mortar. 



Another very extraordinary means of making this change in bodies, which 

 abound in calx or earth, is by fire, not by the intense one that calcines, 

 but by a moderate heat; their most perfect resistance, or non-conducting pro- 

 perty, being when their heat is just tolerable to our hands. Mr. D. had some 

 of the same Portland stone, wrought into plates nearly as thin as window-glass, 

 which he heated to a proper degree, and then coated on both sides with metal, 

 in order to make the Leyden experiment. When the stone is hot enough to 

 singe paper, it conducts as perfectly as when cold ; but on cooling a little, it 

 begins not to conduct, and affords small shocks, which gradually increase in 

 strength for about 1 minutes ; at which time it is about its most perfect 

 state, and remains so near a quarter of an hour : after that time the shocks 

 gradually decrease as the stone cools, till at last they quite cease, and it re- 

 turns to its conducting state again ; but this state appears before the stone is 

 quite cold. 



Experiments of this kind succeed in all bodies abounding in calx or earth, 

 as stones dried clay, wood when rotten or burned in the fire till the surface be- 

 comes black. Among other substances, he tried a common tobacco-pipe, part 

 of which near the middle he heated to a proper degree, and then applied one 

 end of it to the electrified bar, while the other was held in the hand ; and he 

 observed that the electric fluid passed no farther along the pipe than to the 

 heated part. 



XIV, The Case of Wm, Carey, aged IQ, ivhose Tendons and Muscles were 

 turning into Bones. By the Rev. fVilliam Henry, D. D., F. R. S. Dated 

 Castle-Caldwell, near Enniskillen, March 1, 17 5Q. p. 89. 



Wm. Carey was born in an island in Lough Melvill, a large lake in the nor- 

 thern point of the county of Leitrim in Ireland, and had continued there, or in the 

 adjacent lands ever after. He was bred up to work as a labourer, and continued 

 in very good health from his birth until '2 years before the above date. About 



