I 4002 ) 
if their diftance be fo grcatjthat colours begin to appear in the 
light before its incidence onthefecondPnfm, thofc colours 
will not be deftroyed by the contrary refractions of thacPrifm. 
Thefe things being obfcrved^the round image Qwill appear 
ofthe fame bignefsj which it doth when both the Prifmsare 
taken away5that the light may pafs directly towardsQJrom the 
hole without any refraciionat all. And its diameter will equal 
the breadth ofthe long image PT, if thofc images be equally 
diftant from the Prifms* 
If an accurate confideration of thefe refraftions be defigned, 
it is convenicntjthat a Lens be placed in the hole F,or immedi^ 
ately after the Prifms/o that its focus be at the image Qv)r PT. 
Forjthereby the Perimeter ofthe imageQand the ftraighc fides 
ofthe image PT will become much better defined than other- 
wife. 
AnAccountof a Stone cut out from under ths tongue of a Man -Jate^ 
ly lent ^ Letter of Mr, Lifters to his Grace the Lord Arch- 
Bilhop <>rYork. 
May it plcafe your Grace, 
IN obedience to your Grace's Commands,! have penned the 
Circumftances of a not common Medical obfervation,viz. 
the Excifion ofa ftone from under the tongue. And I here with 
prefent your Grace alfo with the ftone its felf, as 1 had it from 
the perfon it Was taken** 
As to the occafion and time of its birth^he tels 
7i^»/> Stem u now fQe/Mv Lord,you may be pleas 'd to give firm 
in the cufiody ofthe j-^ ^ i ..i ^ u u u / 
IT, Society , t0 Credit to every particular^that he hath anl wer- 
whom it reas pre- jjjg J OUT Grace V xoftance) it was from a 
fintcdafterr^ards. ^j^tct Sca-voyage , which bftcd much longer 
than he expected, and wherein he fuflfered an exceeding cold; 
and that, not long after his landing, he found a certain Nodus 
or hard lump in the very place whence this ftone was cut.There 
was about 8 years betwixt its breading and being taken away. 
As to its growthjand the inconveniences thence cnfuing 5 he 
further laith^that upon all frefli= cold -taking, he fuffered much 
pain in that part ef pecially, and yet,that cold once being over, 
that part was no more painful than the reft of his mouth. He 
adds, that towards the and S^Ayeair itdidoftetJ caufefud. 
dca 
