40S Addiiional Notes, 



ascension between the moon and a star, if that should prove prac- 

 ticable with sufficient exactness, would undoubtedly answer the 

 intention of all that is to be expected from the moon, if her place 

 were taken on or near the meridian. But to keep the arch of 

 this instrument in the plane of the equator, and at the same time 

 view two objects of unetjual altitudes, and considerable distance 

 from each other, by the edges of two sights, with the necessary 

 accuracy, will not perhaps be so easy in practice as he would 

 have it believed. 



I shall, therefore, here presume, from thy favour shown me in 

 England, in 1/24, to comnmnicate an invention that, whether it 

 answer the end or not, will be allowed, I believe, to deserve thy 

 regard. I have it thus : 



A young man, born in this country, Thomas Godfrey by name, 

 by trade a glazier, who had no otlier education than to learn to 

 read and write, with a little common arithmetic, having, in his 

 apprenticeship with a very poor man of that trade, accidentally 

 met ;viih a mathematical book, took such a fancy to the study, 

 that, by the natural strengtli of his genius, without any instructor, 

 Jie soon made himself master of that, and of every other of the 

 kind he could bnrrov/ or procure m English; and finding there 

 was more to be had in Liiiin books, under all imaginable dis- 

 couragements, a})plied himself to the study of that language, till 

 he could pretty well understand an author on these subjects ; 

 after wliich, the 'first time I ever saw or heard of him to my 

 knowledge, he came to borrow sir Isaac Newton's Principia of 

 me. Inquiring of him hereupon who he was, I was indeed asto- 

 nished at his re(jue.';t ; but after a little discourse he soon became 

 v/clcome to that or any other book I had. This young man, 

 about eighteen months since, told me he had for soitie time been 

 riiinking of an instrument for taking the distances of stars by re- 

 iiecting speculums, which he believed might be of service at sea j 

 and not long after he showed me a common sea quadrant, to which 

 he had fitted two jjicces of looking-glass in such a manner as 

 brought two stars, at almost any distance, to coincide j tlie one 

 b)' a direct, the other by a reflecting ray, so that the e3'e could 

 t^ikt^ them both tc/^cther as joined in one, while a moving label or 

 index on the graduated ar(.'li marked exactly half their distance : 

 for 1 need not say that the variations of the angles of reflexion 

 irom two speculums are double to the angle of the inclination of. 

 their planes, and therefore give but half the angle or arch of the 

 tii.it;-4;t.«^*, v.hich is the only inconveniency that appears to me to 



