a New H^drojlatic Pnfs, 3 1 



prcfs, tlifi fcrew of v/hicli was iron, and nearly of the climenfioiis before mentioned, except- 

 ing that the lever was twelve inches long inltcad of four inches, and the aftion on the lever 

 upwards of two hundred weight, applied with a jerk, the cffefl; was nearly the fame. Here 

 I Ihould eRimate the advantage to be very much in favour of the hydraulic engine. 



In another engine of this kind, the diameter of the great piflon was four inches, and of the 

 fmaller three-eighths of an inch ; and the advantage given by the lever or handle was twelve to 

 one. Above thepillon of the great cylinder was applied a long lever, at one end of which was 

 an axis, and at the other end a large fcale to hold weights : it contained twenty hundred 

 weight. The diftance between the axis of motion of this lever and the part where it a£led 

 on the piflon was fix inches ; and the diftance from the fame axis to the extremity where 

 the fcale was hung, was 126 inches. Every hundred weight in the fcale confequently preded 

 upon thepillon witha force equal to\t\venty-one hundred weight ; whence the whole preffiire 

 was twenty-one tons. It was eafy to work the lever brillcly with one hand, and each flroke 

 raifed the fcale near one-third of an inch. Forty-fevcn pounds hung at the end of the 

 lever, carried it down with a- moderate fwiftnefs of working; but a weight of only-forty- 

 three pounds remained in equilibrlo, and did not defcend. Now, as the true weight in 

 tlieory was thiny-two pounds, as deduced from the a£lion of the parts in the manner al- 

 ready done with regard to the fmall machine, it follows that lefs than one-third of the aftual 

 power was employed to give velocity and overcome all friction. 



It may be remarked, that the principal frictions in thefe machines mnfl be at the circum- 

 ferences of the piflons, and that thefe do not irrcreafc in the fimple, but in lefs than the 

 fub-duplicate ratio of the power. For if the diameter of the great cylinder were double, 

 every thing elfe remaining unchanged, the furface of its piflon, and confequently the power, 

 would be quadrupled. But the friflion would be only doubled, and that merely at the lea- 

 thering of the greater pillon. 



As the preflure in the experiment lafl mentioned amounted to 47040 pounds upon the 

 great pillon of four inches diameter, or fixteen circular inches furface, it amounted to 2940 

 pounds upon each round inch. But the medium preflure of the atmofphere on a round 

 inch is near twelve pounds, confequently the aftion was equal to 245 atmofpheres : and as 

 each of thefe correfponds with a column of 34 feet of frelli water at a medium, the water 

 in the cylinder was prefled in the fame manner as if the wliole column had been 8330 feet, 

 or I J mile, long. 



Large prefles of this con(lru£lion are made with two pumps of li inch bore, and a cy- 

 linder of feven inches. Thefe have been ufed in prefling hay and cotton for package ; 

 and, as I am informed, arc efleftive in producing a greater condenfation on the material with 

 a much lefs application of moving power and confumption of time. But of this and other 

 particulars, as I have not yet had an- opportunity of examining the fa£ls myfelf, I fliall for- 

 bear to fpcak at prcfent *. 



» Mr. Bramali, wlio conftruftsihtft engines, liasobtaHud a fotcnt fof ilic invcnrion. 



VIII. The 



