226 Pump with two Pistons. [Book II .
subsequently found in Pompeii ) not a few of its diversified modificationswere anticipated by Greek and Roman machinists. Why then were theynot preserved or continued in usel For the same reason that the oldpump is still generally preferred: and were it not for the art of printingit is probable that not one of the modern improvements of this machinewould be known 2000 years hence, any more than those devised by theancients are now known to us. Those persons who are familiär with it,well know that a large majority of its supposed improvers, have returnedfrom long and laborious mental pilgrimages in its behalf, laden, like olddevotees, with little eise than Stores of worthless relics.
Of innumerable variations in its construc-tion, the greater part consists of differentmodes of communicating motion to the rod,by wheels, cranks, racks and pinions, cams,plain and jointed levers, pendulums, balancepoles, vibrating platforms, &c. Of these itwould be useless to speak. Others consist intwo ormore suckers in the same cylinder; inaltering the form of the latter ; and some inimparting motion to the cylinder, and dispen-sing with the sucker. We shall notice someof these here, and others in the next Book .
The introduction of two suckers or pistonsinto one cylinder has long been a favoriteproject. Dr. Conyers in 1673 proposed apump of this kind. He made it of plank,square and tapered, (in the form of an inver-ted and truncated pyramid,) 8J feet long, 20inches square at the upper end, and 8 at thebottom where the valve or lower box wasplaced. He fixed two suckers on the samerod, one at its lower end and the other so asto play half way down the trunk. This pumphe said, raised “at least twice as mach wateras the ordinary one of the same size.” Ifsuch was the fact, it was by the expenditureof twice as much force. Had the bore ofthe trunk, where the upper sucker played,been uniform throughout, and the lowersucker laid aside, and with it the force ex-pended in moving it, the result would clearlyhave equalled that of both. Phil. Trans.Abridg. Vol. i, 546.
About the year 1780, Mr. Taylor of South ampton , Eng. introduced two suckers or pis-tons into one cylinder, each united to a separate rod, that one might as-cend as the other descended, and thus discharge double the quantity ofwater: No. 91 is a figure of it. The rod of the lower sucker slidesthrough the centre of the upper one; and also through its valve, whichis a spherical or hemispherical piece of brass, placed loosely over its seatand to which the rod acts as a guide. The upper parts of the rods ter-minate in racks, between which a cog wheel is placed, having an alternatemovement imparted to it, by a lever attached to its axis, as in the commonair pump.
Another mode of working this pump, is by means of a drum fixed to-