MODIFIED by COMPRESSION. 93 



tapering from 1 inch to 0.6, Their thicknefs was about 0.3 

 at the breech, and tapered towards the muzzle to the thinnefs 

 of a wafer. 



I now adopted a new mode of operation, placing the tube 

 vertically, and not horizontally, as before. By obferving the 

 thin ftate of borax whilft in fufion, I was convinced, that it 

 ought to be treated as a complete liquid, which being fupport- 

 ed in the courfe of the experiment from below, would fecure 

 perfect tightnefs, and obviate the failure which often happen- 

 ed in the horizontal pofition, from the falling of the borax to 

 the lower fide. 



In this view, (fig. 16.); I rilled the breech in the manner 

 defcribed above, and introduced into the muzzle fome bo- 

 rax (C) fupported at the middle of the tube by a quantity 

 of filex mixed with boitle-glafs (B). I placed the tube, fo 

 prepared, with its breech plunged into a crucible filled with 

 fand (E), and its muzzle pointing upwards. It was now my 

 object to apply heat to the muzzle-half, whilft the other re- 

 mained cold. In that view, I conftru&ed a furnace (fig. 14. 

 and 15.), having a muffle placed vertically (c d), furround- 

 ed on all fides with fire (e e), and open both above (at c), 

 and below (at d). The crucible juft mentioned, with its 

 tube, being then placed on a fupport directly below the ver- 

 tical muffle, (as reprefented in fig. 14. at F), it was raifed, fo 

 that the half of the tube next the muzzle was introduced into, 

 the fire. In confequence of this, the borax was feen from 

 above to melt, and run down in the tube, the air contained in 

 the powder efcaping in the form of bubbles, till at laft the 

 borax flood with a clear and fteady furface like that of wa- 

 ter. Some of this fait being thrown in from above, by means of 

 a tube of glafs, the liquid furface was raifed nearly to the muz- 

 zle, and-, after all had been allowed to become cold, the po- 

 fition of the tube was reverfed ;', the muzzle being now plun- 

 ged 



