The First Steam-Boat

< 56 ; Fluid would in whofe placeiti'siubftituted. Were there any neceflity of proving this by Experiment, it might be done thus • Take afmall Olafs Bolt-head (which were it Solid and of a Lump wou’d be near three times heavier than Water, but being hol- low'anol full of .Air only, immerfe and Swim,) this may be -fo nicely fill’d W-Hh ‘Water by the $tem that at the +op of a Jarit may Swim, in the middle it may remain at a Poiie, and put beyond that it will Sink. This will be brought about by the Spring of the Air include<1 therein, which being Compreffible, will either contrat or dilate itfèlf, according, to the Degree øfPreffure -’tis under-, Toward the up- per part of the Jar, twill be prefied by little more than the T^nnofphere« toward the middle, by the Atniolphere and Come Inches perhaps of Water, and at the Bot- lom. by more Water ftill. In the firft Cafe the TVir in the Machine cannot be fo much preis’å a$ in the fécond, in the -fécond not fo much as in the laft $ whence the Mouth of the Machine being un- ilop’d, as the Preflure is increafed, more Water will be gradually thruft into it, making the whole Specifically moreHea- vy, and (o will produce the afore-mention - eJ JEffeét •, which will be viable, tried on aJVfachîtie that is Cmall,