Additional Notes. 47^; 



to answer what is proposed, as it may be framed lighc and 

 ;2asily manageable, thou wilt then, with thy accurate tables, 

 have obtained the great desideratum, and all that can in this 

 way be had from our satellites. And if the method of dis- 

 covering the longitude by the moon is to meet with a reward, 

 and this instrument, which, for all that I have ever read or 

 heard of, is an invention altogether new, be made use of, 

 in that case I would recommend the inventor to thy justice 

 and notice. He now gets his own and family's bread (for 

 he is married) by the labour of his own hands only, by that 

 mean, trade. He had begun to make tables of the moon, on 

 the very same principles with thine, till I lately put a copy of 

 those that have lain so many years printed, but not published; 

 with W. Inny's, into his hands, and then, highly approv- 

 ing them, he desisted. We both wish very much to see thy 

 tables completed, and ushered into the world by thy own 

 hand. On the receipt of this I shall hope for a line, with 

 thy thoughts on it, which, however they prove, will afford 

 a pleasure to 



Thy friend, 



J. LOGAN, 

 Pennsylvania, May 25, 1732. 



From the American Magazine for August, 1758, p. 528. 



To the Royal Society, 

 Gentlemen, 



As none are better able than the Royal Society to prove 

 and judge whether such inventions as arc proposed for the ad- 

 vancing useful knowledge will answer the pretensions of the 

 inventors or not; and as 1 have been made acquaimed, though 

 at so great a distance, of the candour of your learned society 

 in giving encouragement to such as merit approbation, I have, 

 therefore, presumed to lay before the society the following, 

 craving pardon for my boldness. 



Finding by what difficulty a tolerable observation of the 

 sun is taken by Davis's Quadrant, and that in using it, 

 unless the spot or shade be brought truly in the line of the 

 horizon-vane, the observation, when made, is good for no- 

 thing; to do which requires much practice, and, at best, is 

 but catching an observation ; and considering further the small- 

 jiess of the 60 deg. arch, and the aptness of wood to cast, 

 yvhich makes often little better than guess-work ; I iherefoxe 



