| Beth Ailgeiblelvee tare vi ok “ie nome ‘ 
~ with Cement or Glew is faftned the piece o 
ferbe.) that thelines of the angles,o 
Peer wee ee 
The Part xc. | 
nos 5, Sarees all sige 
betweenan inch and:a foot, one for all Glaffes between a foot and ten foo: 
long, another for all between'ten arid an hiindred.a fourth | — between a 
hance ‘and avthoufand foot’ longs: and if \Guriofity thall.'e rocee fa 
tie for all lengths between a howiiod and ten thoufand | foot ong ; 
ine poe 3¢ Ng ciple is en a bi er ‘the Afaddrils well made,and 6F a 
nd Yuppo re be: uféd vin working sand « polifhing 
Shediac nthe et +p ua a erat of. thoufand.nay of, te . thoufand: oak 
long, may beas well rmadeasone of ten; for ‘the realon is the-fame flap 
the Mandils arid‘ Tools be’ made® fufficiently. ftfong; {o'thatthey hee 
bend; \and fappofing the Glafs, eutef which they are wrought, si tees 
of fo great a regularity in\its parts 4s to refraction : this hallow Cylinder K 
isto contain the Sand, and by being drove rotind Very quick 6 and fio by: 
means of a {mall Wheel, which ma may be moy/diwithones foot, ferves to grind. 
the Glafs: The other 4@zndril is thap'd like this, -buti it baka even neck.in- 
ftead of a taper one,and runs.in,a Collar, ner Be by the help of ‘a Screw, and.a 
joynt made like/M in the Figure, itcan be {till ad jp 0 to,the, wearing or 
‘wafting neck : into the end of thineitendr its istered Gln a Chock N, onwhick, 
pape Q. that I be formd; 
the middle of which Gla&. is'to be. pag djuft, onthe edge.of th phe Bing, and. 
the Lath O P. is to be fet and fixe, ( nie yi) “es and i Ss, 
the shanner whereof will be. fufficiently eyidenc: , 
an Angle asis ‘nequifite to the. forming of fucha. mek de-. 
fign'd to be of 5, the geometrical ground of which being Pie aa 
though not heeded before, I thall, 63 brevities. fake, pals over. . This lait, 
Mandrilis tobe made ( by meangot, the former, or, fome, other wheel J to: 
_ tum round very fwift, alfo, by, which two. asia tu tae the, Glafs oe 
chute: (if care -be hase ‘but bbe FONE into amoft, ge y. toh 
Sesskabt. To Al 2 ‘ ys38tq wins s Gt 4 | go? wy tor- 
5 ies 3 
But hana oe are certs Bo am the Laws.of refrattion. é ‘ohh i 
Pie experiinerttally found taB® fo,by an 1 Infirument I poall prefently de- 
of Angidence, ave propoitio-’ 
nate tothe ret of the Se mney yr if Gloflescould 
be made thole’kind of Figures, or ome other, fuch asthe’ into a~ 
rable Des Cera ine il a Sy bis Ph 5 ii 
thematical Works,we might bo bipe for ch greater per ) ion of Opti ticks’ 
aren lacy opt fi fs. SRO 
bas, we, id, that the larger the Teléoe Objeti Gheaffes ar 
