Page:Philosophical Transactions - Volume 002.djvu/59

tise of Opticks ready for the Press; but though I have used my utmost endeavour to retrieve it, yet I have in that point been totally unsuccessful: But some loose Papers and Letters I have, particularly about this Instrument for taking of Angles, which was far from perfect. Nevertheless, I find it so much to exceed all others, that I have used my Endeavors to make it exact, and easily tractable; which above a Year since I effected to my own desire, by the help of an Ingenious and Exact Watchmaker in these Parts: Since which time, I have not altogether neglected it, but employed it particularly in taking the Distances (as occasion served) of the Circum-jovialists, towards a perfect setling their Motion, I shall only say of it, That it is small, not exceeding in weight, nor much in bigness, an ordinary Pocket-Watch, exactly marking above 40000 Divisions in a Foot, by the help of two Indexes; the one shewing hundreds of Divisions, the other, Divisions of the hundred; every last Division, in my small one, containing, ${\tfrac {1}{10}}$ of an Inch; and that so precisely, that, at I use it, there goes above 2½ Divisions to a Second. Yet I have taken Land-Angles several times to one Division, though (for the Reason mention'd by M. Auzout) it be very hard to come to that Exactness in the Heavens, Viz. The swift motion of the Planets. Yet, to remedy that Fault, I have devised a Rest, in which I find no small advantage, and not a little pleasing those persons who have seen it, being so easie to be made, and by the Observer manag'd without the help of another: Which second Convenience, my yet nameless Instrument hath in great perfection, and is, by reason of its smalness and shape, easily appliable to any Telescope. Sir, 'If you think this Invention, thus improv'd, worthy to be taken notice of by the Curious, you may ** Care is taken, to get both his Description, and the Observations, from M. Townly. command a more perfect Description of it, or any of the Observations, either M. Gascoigne, or my self have made with it.

More