AcliUtional Xutes. 



41, 



judge whelher such inventions as are proposed for the advancing 

 useful knowledge will answer the pretensions of the imcnlors or 

 not J and as 1 have been made acquainted, though at so great a 

 distance, of the candour of your learned society in giving encou- 

 ragement to such as merit approbation, 1 iuive tl)crefore pre- 

 sumed to lay before the society the following, craving pardon for 

 my boldness. 



Finding with what difficulty a tolerable observation of die sun it 

 taken by Davis's quadrant, and that in using it, unless the spot or 

 shade be brought truly in the line of tlie horizon-vane, the obser- 

 vation, when made, is good for nothing; to do which requires 

 much practice, and at best is but catching au observatiouj 

 and considering further the smallness of the ()0 deg. arch, and the 

 aptness of wood to cast, which makes often little better than guess- 

 work ^ J therefore applied my thoughts, upwards of two years, to 

 find a more certain instrument, and contrived the following im- 

 provementj as I think, in the make and use of the bow; r/x. 



The quadrant is to be numbered from each end to 90 at the 

 ether, as in the figure. The sight and glass vanes are the same 

 with the common, excepting that the glass should be larger, and 

 1 think it would be better if ground to the segment of tJie cylin- 

 der. The horizon-vane should be like that of the figure tliereot ; 

 having three holes, IKL; one hole, I, to tit on the centre of tlie 

 quadrant. A; the otlier two, KL, to see the horizon through, 

 whose length across the vane may be one-eighth of the radius 

 AB, or more ; the horizon-vane should be a little hollowed, an- 

 swerable to the curvature of the circle DAK, or cylinder, wliose 

 semidiameter, AJT, is about seven-elevenths of AB, the radiu:, of 

 the quadrant. 



In observing with thifj quadrant at sen, let the sight and glaM 

 vanes be kept nearly on the same numbers, or at equal distances 



