of ascertaining the Magnitude of small celestial Bodies. 33 
the little notch in the pin’s head between the coils of the wire 
making the head, appeared like a narrow black belt sur- 
rounding the pin in the manner of the belts of Jupiter. This 
notch by the microscopic projection measured ,00475 inch ; 
and subtended an angle, at the centre of the mirror, of 
With 303,5 I saw the belt still better, and could follow it 
easily in its contour. 
With 432,0 I could see down into the notch, and saw it well 
defined within. 
With 522,3 the pin’s head was a very striking globular 
object, whose diameter might easily be divided by estimation 
into ten parts, each of which would be equal to o'', 364. 
With 925,6 I saw all the same phenomena still plainer. 
The result of this experiment is, that an object having a 
diameter ,0425 may be easily seen in my telescope to be a 
round body, when the magnified angle under which it appears 
is a' 18", 9, and that with a high power a part of it, subtending 
an angle of o",g6/^ may be conveniently perceived. 
When I considered the purpose of this experiment, I found 
the result not sufficient to answer my intention ; for as the size 
of the object I viewed obliged me to use a low power, a doubt 
arose whether the instrument would be equally distinct when 
a higher should be required. To resolve this question, it was 
necessary either to remove my objects to a greater distance, 
or to make them smaller. 
2 d Experiment, with small Globules of Sealing-wax. 
I melted some sealing-wax thinly spread on a broad knife, 
and dipt the point of a fine needle, a little heated, into it, which 
took up a small globule. With some practice I soon acquired 
mdcccv. F 
