[ 1° 6 ] 
flruCted in the common manner, with three eye- 
glafTes, the field is always very much contracted. 
Thefe confederations, Sir, firft fet me on contriving, 
how to enlarge the field by increaiing the number of 
eye-glaffes, without any hindrance to the diftinCtnefs 
or brightnefs of the image : And tho’ others had been 
about the fame work before, yet obferving, that the 
five-glafs telefcopes, fold in the fhops, would admit of 
farther improvement, I endeavour'd to conftruCt one 
with the fame number of glafTes in a better manner ; 
which fo far anfwer’d my expectations, as to be al- 
low’d by fuch perfons, as are the beft judges, to be 
a confiderable improvement on the former. 
Encouraged by this fuccefs, I refolved to try, if pof- 
fibly I might gain fome farther enlargement of the 
field by the addition of another glafs : and by placing 
and proportioning the glafTes in fuch a manner, as to 
correCt the aberrations as much as poflible, without 
any detriment to the diftinCtnefs, I have obtained as 
large a field, as is convenient or neeeffary, and that 
even in the longeft telefcopes, that can be made. 
Thefe telefcopes with fix glafTes having been well 
received, and fome of them being gone to foreign 
parts, it feems a proper time to fettle the account of 
its origin ; which is one of the motives, that has in- 
duced me to trouble you with this fhort fketch of 
the confiderations, that gradually led me to its con- 
ffruClion j and I am emboldened, Sir, to write thus 
much, from the many favours I have already re- 
ceived at your hands, as well as from a fenfe of your 
being a proper perfon to judge in fuch cafes. And 
tho I atn fenfible, that you are not unacquainted 
with the theory contain'd in this letter, yet foraf- 
mucli 
