( *24) * 
l wiCh-j I had a fecret in optic ks to encourage him to that 
communication, it I did believe, that this would be eftee- 
med one. To meafure with a great let eft ope rhe dihance of 
Obje&s upon rhe Earth 5 which I have found long fince, and 
pro poled to fome by way of Paradox* Locorum dtjtuntias 
txumca ji*tione 9 abfque ullo Injlrum nto Atathefnatico 9 wetirt$ 
1 doe here promife to difeover it to him, with the neceffary 
Tables, as foon as He. (hall have imparted his to met which 
I will ufe, as he (hall order me. For, a i hough the Pra&ife 
doe not altogether anfwer the iheoryrf my Invention, be- 
caufethat the length of the Telef copes admits of fome Lati- 
tude * yet one comes near enough, and perhaps as Juft, as 
by moft of the wayes, ordinary ufed with Inftruments. 
That, which I am propofing, i doubt not but M. Hook will 
foon underftand, and fee the determination of all Cafes 
polsible. I (hall only fay . h at if we look upt n he foie 1 he- 
ory , we may make ufe of an ordinary lelefcope , whereof the 
Eyt-glafs is to be Convexe {for, by putting the Glades at a lit- 
tle greater diftance, than they are, p oportionably to the 
diftas icefor which it is to ferve , and by adding ro it a new 
Eye* glafr 9 the Objed will be teen diftind, though obfeure 3 
and if rhe Eye-glafs be Convexe the Objed will appear ered. 
They may be done two manner of ways 5 either by having 
the Lelefcope in. its ordinary (ir nation , rhe objeU-gUfs before 
the Fye-glafs j or by inverring ir, and purring this before 
tk t. But if any will make ufe of two Objefr glajj> where- 
of the tonus's are known, the diftance of them will be 
known. If it befuppofed, that the Focus of the firjt be B. 
and that ofth c fecond C, and rhe diftanceg*ven, B + 2 D, 
and that D minus C be equal to F 5 for. this diftance will he 
equ .*>/ 'o B 1 C + F- • r F *C a And ir you have the Fochs of the 
firf O je& glafti e qua! to B the diftance, where you will 
put frh eferond Glafs equal to B f C t D. the ficus of the 2d 
Claffe will be found equal ro ^3 And if you will that rhe 
O^jed (hall be magnified as much, with tbefe two G’a(Tes 3 
as it would be with a jQngle one 5 whereof the Focus 
/ (hould 
