AND EXTERNAL RESISTANCE. 289 



is of no consequence ; it must be equally ob- 

 vious, that the resistance within, not being 

 equal to the pressure without, the fluid would 

 necessarily be forced up the tube, until the con- 

 densation of the air within it was equal to the 

 air without it, and an equilibrium obtained; and 

 we may a fortiori conclude, that the degree of 

 elevation of the fluid within the tube would in- 

 crease in proportion to the degree of rarefaction 

 which could be accomplished. 



6. It is obvious, that by the abstraction of the 

 air, as far as was possible, out of the vessels men. 

 tioned, the diminished pressure within, which 

 was in consequence produced, would enable the 

 external pressure upon them from without, prc 

 gressively to increase ; the consequence would 

 be, that the glass receiver would be more firmly 

 fixed to the pump-plate ; that the bladder upon 

 the cylinder, instead of being simply depressed, 

 would be pressed upon with such an increased 

 force, that it would actually burst ; and that 

 the exhausted tube, whether made of glass, 

 iron, copper, or wood, immersed in the water, 

 or mercury, wotild have these fluids, by the 

 pressure of the external air, forced up to a 

 higher point of elevation than before, in the 

 unresisting medium which the tube contains. 



It is owing to the same cause, to the dilata- 

 tion of the surrounding medium, that the va- 



