II 
[ i8o ] 
Ij' fingle eye-glafs, in the manner of a common refract- 
ing aftronomical telefcope ; but with this advantage, 
that, as the images will be exhibited larger and dif- 
tinCter by the reflecting telefcope ; and as every part 
thereof will be much more manageable than a long 
refracting telefcope; fo the contaCt or coincidence of 
the images will be more accurately obferv’d. 
It would be however unnecelfary now, as well as 
improper, to fay much about the advantages of this 
method above thofe, which have hitherto been put 
in practice ; becaufe, as a machine is now making 
for this purpofe, the experiments, which will fhortly 
be tried, will be more convincing, as well as more 
intelligible, than any thing that might be offer’d at 
prefent. 
Ex plana tioji of the Figure.. 
The two femicircles reprefent the two fegments qF 
the objeCt-glafs, whofe centers C and D are drawn 
off to the diftance C D y and the poiats viand B are 
two objeCts, or different parts of the fame objeCt ; 
therefore the lines A CG and B DG reprefent two 
■ rays that pafs thro’ the centers or poles of the feg- 
ments, and are therefore not at all refraCted, but go 
ftrait through to G, where they interfeCt j and G being 
the refpeCtive focus to the diftance of the objeCts 
from the glafs, the two images will coincide at that 
point. It appears from the figure, that AB : CD 
G H\ GE ; and from a common proportion in optics, 
GH : G E :: H E : E F. Therefore, AB : CD ; : 
HE : EF-, F being the focus of parallel rays ; and 
confequently 
