LETTERS ON SCIENTIFIC SUBJECTS. 69 



siructions from you to satisfye Sir Charles in the matter of 

 that calculation ; nor the effects of the glass focus according 

 to the measures of it. The doubts we conceive of its effects, 

 supposing the calculations right, are these. 



1. How clere vision can be made, by beanies tending to an 

 angle in the eye : for this seemes contrary to one of the theo- 

 remes undemonstrated in your other tract : but your glass 

 drawes the beames to an angle on the eye. 



2. How one beame can be sufficient to cause cleare vision 

 of the point whence it comes ; for soe your glass seemes to 

 be calculated, to refract ordinately but one beame from one 

 point of the object. 



3. But if you say the glass so formM will convey all the 

 beames falling on it from one poynt ordinately to the eye, 

 this would be well demonstrated ; for else it would cause con- 

 fusion, and so destroy, if not all, at least clere and distinct 

 vision. 



4. Lastly, supposing all before were made good ; the ques- 

 tion is whether the hand or toole of any artificer be able to 

 worke the formes or moulds, and consequently the superficies 

 of the glass soe true, as that to nature they shall be distin- 

 guished from other convexe superficies, as the spheriques, 

 coniques, &c. 



Sir, I know it is a difficult taske for you to treat by letters, 

 but since we have yet no other way, and that the infectious 

 ayre hinders both yours and my gooing to London, where we 

 might meet to consider how to bring this to some good pass, 

 I desire you to doe us the favour, in the meane while, to write 

 to us as oft as you can. 



I heare Mr. Hobbes is expected, with his charge, very 

 shortly. I doubt not but he will finde you out ; and by him 

 you may send your letters to us, if you can finde no other. 

 Or if you send your packett to one Mr. Boothe, steward to 

 the Countess of Devonshyre, at Byflett, nere Oatlands, to be 

 sent by him to me at Welbeck ; in regard of messengers that 

 pass between them and us, your letters will come to us that 

 way. 



Sir, I beseech you present my humble service to the noble 

 knight and lady, where you are, as also to Mr. Aylsbury and 

 Mr. Hyde, with my hearty thanks to them for their favours. 

 Soe God keepe you and 



Your faythfull friend and servant, 



ROBERT PAYNE. 



