i 4CD2 ) 
if tlieir diftance be fo gre^t^that colours begin to appear ia the 
light before its iBcidence oti thefecond Prifnij thofe colours 
will norbeUeftroyed by thp contrary refraccions of chacPrifm,. 
Thefe thlogs being obferved.the round image Q^will appear 
oftlie fimebignefsj which it doch when both the FriTmsare 
takea awayjthat the light may pafs directly towardsQTrom the 
hole without any refradion at all. And its diameter will equal 
the breadth of the long image PT, if thofc images be equally 
diftant from the Prifms. 
if an accurate confideration of thefe refraftious be defigned^ 
it is convenientjthata letu be placed in the hole F,or immedi- 
ately after the Prifms^fo that its focus ho at the image Qor PT. 
Forstbereby the Perimeter of the image Qand the ftraight iides 
ofthe image PT will become much better defined than other- 
wife. 
AnAccountof a Stone cut Qutfrommder the tongue of a Man ^ late-, 
ly (ent ^ Letter of Mr, laiUcn (e his Graee the Lord Arch- 
Brlhbp «f York. 
May it pleafe your Grace^ 
IN obedience to your Grace's Commands,! have penned the 
Circuraftances of a not common Medical obfervation, viz. 
the Excifion of a Jlone from under the tongue. And I here with 
prcfent your Grace alfo with the ftone its felf^ as I fead it from 
the perfon it was taken^"^ 
As to the occafion and time of its birthjhe tels 
«^^^C^*y Lord,you may be pleas'd to give firm 
i?. Societj , u Credit to every particular^that he hath anfwer- 
whomkwas pfy^ gd me at jour Grace s inftance ) it was from a 
' winter Sea- voyage, which lajftedmuch longer 
than he expcftedj and wherein he fulFered an exceeding eold^ 
and thatj 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 betwist its breading and being taken away. 
As to Its growthjand the .incoDvcoiences thence cnfuing 5 he 
farther faithjthat upon all frefli= cold- taking, he fuffcred much 
painia that part efpecially^ and yet^thatcold once being over, 
thatpart was^ no more painful than the reft of his mouth. He 
a^df, that towards the 7^^; and ^tl yetr^it did-often caujfe fud^ 
den 
