STATICAL LAMP. 1(>7 



a neck or pipe D, proceeding downwards nearly to Its bottom ; Dcfcriptlon of a 



but there is a communication with the External iii', through ^i^^ip, 



perforation (reprefented by afmall fliadcd circle near B) which 



prevents the almofphere from interrupting the intended aflion. 



The lightly fliaded femicircle B reprefents an hemifpherical 



fblid capable of revolving on an horizontal axis, fo as to hang 



downwards and fill the lower half of the globe, when no 



fluid is prefent; or it can be rai fed up by floatage into any 



other pofition, according to the quantity and denfity of any 



fluid that may be poured in. 



Let us now fuppofe the velfel C to contain any fluid not 

 more than half its capacity, and that the revolving piece B 

 is of fuch a weight as to be of half the fpecific gravity of 

 that fluid : it may then be eafily underflood that the piece B 

 will fettle into fuch a fituation as that part of it fhall be im- 

 merfed in the fluid ^nd fupport it in the veHel, exa6t!y to the 

 height of its axis. For the part of the folid, immerfed on one 

 fide, is exadly equal to the fpace above llie fluid in that fitu- 

 ation, on the other fide ; and the greater part of B which is 

 on one fide of the perpendicular will exceed the Imaller part 

 on the other fide, by fxadly double ihat quantity. Confe- 

 quently the immerfed part of the folid will be prefied down 

 by twice its own weight ; and tliis is exadly equal to the 

 weight of fluid which it difplaces; whence the body and the 

 fluid will be in equilibrio. Let us now fuppofe the fluid to be 

 brine, at the fpecific gravity of 12, which may be poured in 

 either at the top or at the fide hole, and that oil of the fpeci- 

 fic gravity of 9 be then poured upon it; and it ■is manifeft 

 that the oil will prefs the denfe fluid upwards into C, as re- 

 prefented in the figure, and that when C is half filled, the oil 

 will ftand at an elevation above the axis equal to one half more 

 than the height of the denfe fluid, meafured from its liirface 

 where the oil prelTes upon it. And, when this afijufiment is 

 once made, by putting in the proper quantity of denfe fluid, 

 if any of the oil be taken out, or conluined by burning, the 

 preflTure will be lefs, and the denfe fluid will rife within the 

 vafe. But this rife will not be attended with any depreflion 

 in the veflel C, becaufe the level will be kept up by the re- 

 volving piece B, and confequently the oil iifelf will be pre- 

 vented from falling as much as it would have done if this con- 

 trivance had not been applied. 



I do 



