IMPROVEMENT IN MR. E. WALKER's QUADRANT, 219 



Plate XL Fig. I. A reprefents part of the engine beam ; 

 B (he connecting rod; C the crank ann; D a cog-wheel, 

 working into another cog-wheel F, of half the fize ; Fa crank 

 arm on the fliaft of" the fmail wheel; G a cylinder clofed at 

 bottom, in which afolid or unperforated pifton moves, leaving 

 a vacuum beneath. This afts limply inftead as a weight on 

 the crank F, by the conftant prelfure of the atmor[)here; and 

 the diameter of the pifton muft be fuch as nearly to equal one 

 third of the power of the engine. 



In Fig. 2. the outer circle is the line defcribed by the crank; 

 the circumference of the inner circle is equal to twice the 

 diameter of the outer, and the fquare has the fame cir- 

 cumference; this laft exhibits the iiiequality ftill remaining, 

 which by this method is reduced to about one fifth ; but by the 

 affiti:ance of a fmall fly on the fecond motion, the efFe6l will 

 become nearly the fame as that of a rotative engine, with the 

 advantages here mentioned. 



The fame motion may be applied to a pump, but in this cafe 

 the two cranks muft be horizontal at tiie fame time. 



I 



XIV. 



Jmprovemeni hij which the additional Arc in Mr. Ezekiel Walker's 

 refieding Quadrant is rendered nnmceffarj/. Jp. a Letter fram 

 ' the Inventor. 



To Mr. NICHOLSON. 

 SIR, 



x\NY one who has a juft idea of the refieding quadrant, Improvements 

 defcribed on page 218 of the fourth volume of your Journal, j^gr'/refleains" 

 will perceive that one half of the arc of that inftrument is quadrant, 

 appropriated folely to the redlifying of the fecond horizon glafs. 

 This method of adjufting is as good as any other that I have 

 to propofe, but it is attended with the inconvenience of adding 

 to the fize of the inftrument, and confequently to its weight. 



The following method of adjufting the fecond horizon glafs 

 will reduce the inftrument to an odant, which will ftill pofTefs 

 the fame property of meafuring any angle lefs than 120° by 

 the fore obfervation. 



Jiifl 



