jo Mr, Wilson’s propofed Experiment , &cc. 
achromatic obje£t-glafs for the fake of a large aperture, and of 
fuch a figure as to fhorten the focal diffance as much as the 
obfervations of fuch a fmall angle can admit of. Some con- 
trivance too will be requifite to keep the whole fpace between 
the objedf-glafs and the eye-glafs always full, notwithstanding 
the expanlions and contractions of the confined fluid by 
heat and cold, or its wade by evaporation. 
It might prove a very conliderable abridgement of the necef- 
fary apparatus, if this kind of telefcope could be connected 
with the common telefcope of a mural quadrant, or zenith 
lector, and their axes made perfectly parallel by previous obfer- 
vations of a proper terreftrial objeCt. But as there would be 
fome room for apprehending that the exact adjuftment of the 
axes might be affected in raiflng the telefcopes afterwards for 
celeftial obfervations, this might be examined into by di- 
recting them to fome ftar lituated in, or very near, the ecliptic, 
and taking its meridian altitudes at a time of the year when it 
is in quadrature with the fun, in which cafe it would have no 
aberration. But either in this way, or with two feparate inftru- 
ments ,the experiment might be made in a few nights, by taking 
the zenith diftance of a proper ffar, the plane of the inftruments 
being alternately turned different ways in obferving, to get 
the true zenith diffance independent of the error of the line of 
collimation ; or the meridian altitude of the pole ffar may be 
obferved in December above and below the pole, which will 
give the apparent diffance of the ffar from the pole at that time 
as affefled by aberration. The error of the line of collimation 
would not affeft the refult in this way, being the fame in the 
obfervation both above and below the pole. 
