412 Additional Notes, 



of the speculum GH is no disadvantage, because the rays comd 

 reflected in the same manner as they come direct. It may be 

 needless to add that, when practicable, the moon should be taken 

 ■when near the meridian — or that the instrument will equally take 

 the distance of the sun from the moon, when visible, as she often 

 is, in the day-time; for which purpose there must be a place 

 made at M for a d^ikening glass, to be fixed there when neces- 

 sary, and the lele cope directed to tlie moon. Nor need 1 add, 

 that the same instrument will very well serve for taking the di- 

 stance of any two stars, a comet, &c., always taking the brightest 

 by reflection ; " all which is obvious. But I must further ob- 

 serve, with pleasure, that if we do not quite mistake in all that 

 has been said here, there is now a method found by it to obtain 

 what is equivalent to a bodily appulse of the moon to a fixed star, 

 or to the sun at any moment when visible, which, indeed, might 

 be wished 3 but if the longitude could ever be expected to be de- 

 termined by the motions of the moon (to which end J. Flam- 

 stead's, and thy more assiduous labours in observing her, have, I 

 suppose, been principally levelled), and this instmment be duly 

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

 easily manageable, diou wilt then, with thy accurate tables, have 

 obtained the great desideratum, and all that can in this way be 

 had from our satellite. And if this method of discovering the 

 longitude by the moon is to meet with a reward, and this instru- 

 ment, which, for all that I have ever read or head of, is an inven- 

 tion altogether new, be made use of, in Uiat case 1 would recom- 

 mend 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 

 oaly, by that mean trade. He had begun to make tables of the moon, 

 on the very san:e principles with thine, till I lately put a copy of 

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

 wath W. Innys, into his hands, and tlien, highly approving them, 

 he desisted. We both wish \ery much to see thy tables com- 

 pleted, and ushered into the world by thy own hand. On the 

 receipt of this 1 shall hope for a line, with thy thoughts on it; 

 wliich, however they prove, will afl^brd a pleasure to 



Thy frienil, 

 Pcwiti/hunla, May 25, 11?>2. , J. LOGAN. 



From the American Mai^azine fcr An^vst, 1758, p. 528. 



To the Jioj/al Sociefj/. 

 Gkntlemkn-, 



As none are better able than the Royal Sociciij to i)rovc and 



