302 - Dr. Herschel’s observations of the satellites 
nient. When the apparatus was preparing, I found that 
handles, 20 feet long, would be very cumbersome, and at- 
tempted to try the micrometer with the assistance of a person 
to arrange the points; but, when engaged in the first mea- 
sure, I found that unless I had myself the command of the 
motions, a perfect adjustment could not be obtained ; or would 
at least take up so much time as would bring on an alteration 
in the telescopic motions, not consistent with perfect vision. 
This micrometer has, however, the peculiar advantage that 
it may be used with a concave eye glass. 
When a satellite is either directly preceding or following 
the planet, its distance may be measured by the difference of 
the time of their passing the meridional wire. This method, 
which has also been tried, is however not sufficiently delicate 
for very small intervals, and is moreover of little use, on ac- 
count of the very limited situations. 
The following observations on the satellites of the Geor- 
gian planet are given in the order of time they were made. 
They contain every thing that relates to the appearance and 
motion not only of the two principal large satellites, that are 
plainly within the reach of a 20 feet telescope of my construc- 
tion, but also the more difficult researches that have been 
pursued for detecting additional satellites. That such there 
are I can have no doubt; but to determine their number and 
situation will probably require an increase of the illuminating 
power, such as I was in hopes, when I published my announce 
of their existence, would have been used by other astrono- 
mers, in pursuit of the subject pointed out to them ; a 23 feet 
reflector which is mentioned in the observations, may proba- 
bly be sufficient for the purpose. 
