VOL. XXXII.] PHILOSOPHICAL TRANSACriONS. 555 



rises in tine said shell, and the base is the area of the shell itself. This weiglit 

 in our engine is equal to 57-5 pounds, and therefore one would think it greater 

 than the resistance made by the friction of a piston. But if it be considered, 

 that in the descent of the barrel for sucking, the mercury shifts immediately 

 into the inner shell, rising to the same height, and still keeping the same base; 

 the aforesaid weight of 57.5 pounds helps down the barrel, and facilitates the 

 overcoming of the force of the atmosphere, consequently the weight of the 

 mercury, being balanced, is no hindrance, whether you work with a single or 

 a double barrel. 



There remains then only the hindrance by loss of time in the beginning of 

 any stroke : but I have showed that to be but -^ part of the stroke. I have 

 found that the best engines now in use generally lose near -f of the water that 

 they ought to give, according to their number of strokes. And Mr. Henry 

 Beighton, an ingenious member of this Society, having a great many times 

 measured the water that is raised by engines in mines, found that some engines 

 lost -f, and none ever lost less than -f, of what they ought to give, according 

 to the number of the strokes in their pumps, whatever auxiliary powers they 

 were moved with. 



There is indeed another objection, but scarcely worth notice; which is, that 

 some particles of mercury will mix with the water that is raised, and make it 

 unwholesome ; but nobody that considers specific gravity, will imagine any such 

 thing. However, to satisfy those that might still apprehend it, it is to be ob- 

 served, that none of the water that is raised comes near the mercury : for in 

 the cylinder c, and part of the elbow b, fig. 5, there is always above the mer- 

 cury a certain quantity of water, that rises and falls with the barrel, and never 

 goes into the forcing pipe. The same happens also in the machine of 

 fig. 6 ; for the water having once run into the cylinder c, all that is raised 

 afterwards, comes through the forcing valve, without coming down to the 

 mercury. 



Provided care be taken to make the barrel with its plug tight, I do not see 

 that this machine will want repair in a long time, except some of the auxiliary 

 powers be out of order, which do not relate to this invention. The numbers 

 given will serve to examine the truth of what I have asserted concerning the 

 motion of the mercury : and from them one may make tables to serve to pro- 

 portion these engines for raising any quantity of water to any height, according 

 to the power to be applied. 



4 B 2 



