1835.] First Astronomer- Royal, 407 



Street, to have been greater at the quartile, or latter time, 

 by about 45" than at the opposition in November, on the 

 contrary it was less by about 1'. 20'. Which showed that, 

 from the opposition to the quartile, she removed from the 

 earth : whereas their theories made her approach nearer to 

 it, making her diameters bigger at the quartile than at the 

 opposition by 1'. 30"; and that they erred also very sensibly 

 in her visible place. 



But, enquiring her visible place and diameters, by the 

 tables I had fitted to Mr. Horrox's lunar theory, I found 

 her place agree nearly ; and her diameter at the full moon 

 bigger than at the quadrature by about 50' : which convinced 

 me that Bullialdus's, Wing's, and Street's theories were 

 erroneous ; and Horrox's near the truth. I did not then 

 think the theory perfectly agreeable ; for I found a dissent in 

 my observations from it, by reason I had not yet attained the 

 the knowledge of a further necessary diminution of her dia- 

 meters depending on her distance from the sun, with which 

 Mr. Newton's corrections and emendations of that theory 

 have furnished me since. These observations I imparted to 

 Mr. Oldenburg, with the same remarks upon them ; which 

 occasioned their joint desires that, now Mr. Horrox's re- 

 mains were in the press, I would add the tables I had fitted 

 to his theory, with an explication of the theory itself, and 

 directions to calculate the moon's places, &;c., by the tables : 

 which I willingly did, fitting the radixes of my mean mo- 

 tions to the meridians both of London and Derby, where I 

 then thought my abode fixed, and hoped to carry on my 

 observations to greater accuracy : for which, in my 

 thoughts, I was frequently forecasting. 



In the spring of the year, 1672, I excerpted several ob- 

 servations from Mr. Gascoigne's and Crabtree's letters, 

 that had not yet been made public ; which I had turned 

 into Latin, and resolved to publish in the first volume of 

 Celestial Observations taken at the Observatory. Amongst 

 Mr. Gascoigne's letters I found some wherein he showed 

 how the images of remote objects were formed in the dis- 

 tinct base of a convex object glass. From these I got my 

 dioptrics in few hours ; having read Descartes' Dioptrics 

 before, but learnt little by them because he discourses not 

 of this subject : his main business being to show how by 



