VOL. I.] PHILOSOPHICAL TRANSACTIONS. 2g» 



is usually in the middle between the sides of the rock, but as near the bottom as 

 may be, it is to be struck upon with a hammer, the heavier the better, either 

 suspended by a shaft turning upon a pin, or otherwise, so as one man may 

 manage the hammer, while another holds the tool or piercer. After the stroke 

 of the hammer, the point is to be turned a little, so that the edges or angles at 

 the point may all strike upon a new place ; by which means small chips will at 

 every stroke be broken off, which must from time to time be taken out, as need 

 requires. And thus the work is continued, till the hole be 18 or 20 inches deep; 

 the deeper the better. To this hole a kind of double wedge is to be exactly fitted, 

 as appears in fig. 4, each piece being 12 or 13 inches long, and so made, as 

 being placed in their due position, they may make up a cylinder, cut diagonal- 

 wise. The two flat sides that are contiguous, are to be greased or oiled, that 

 the one may slip the more easily upon the other ; and one of them, which is to 

 be uppermost, having at the larger end a hollow crease or groove cut into, it 

 round about, for fastening to it, with a thread, a cartridge full of gunpowder, 

 about half a pound or more as occasion may require. This wedge must have a 

 hole drilled through the length of it, to be filled with priming powder, for firing 

 the charge in the cartridge. 



The wedge being first thrust into the hole with the cartridge, the round side 

 where the priming-hole is being uppermost, the other wedge is to be thrust in, 

 home to the due position, observing, that they both fit the hole in the rock 

 exactly. Then, on the end of the lower wedge, which is to be about an inch 

 longer than that of the upper, and flattened, priming powder is to be laid, and a 

 piece of burning match, or thread dipt in brimstone, or other such prepared 

 combustible matter, fastened to it, that may. burn so long before it fire the 

 powder that the workman may have time enough to retire, having first placed 

 a piece of wood or iron so, that one end thereof being set against the end of the 

 lower wedge, and the other against the side wall, that it cannot slip. When 

 the powder takes fire it first drives out the uppermost wedge, as far as it will 

 go, but by the slanting figure of it, the farther it goes backward the thicker it 

 grows, till at last it can go no farther ; then the inflamed powder tears the 

 rock to get forth, and so cracks and breaks it all about, that at one "time a vast 

 deal of it will either be quite blown out, or so cracked and broken, as will make 

 it easy to be removed. 



Observables upon a monstrous Head. By Mr. Boyle. N" 5, p. 85. 



In this monstrous head of a colt, the two eyes were united into one double 

 eye, which was placed in the middle of the brow, the nose being wanting, 

 which should have separated them. Hence the two orbits were united into one 



