384 Dr. Herschei/s Description of a 
the object he wishes to pursue in its course, for as many mi- 
nutes as may be convenient. If, indeed, he is inclined to give 
up the meridian for some time, he may order the whole frame 
to be moved by the great round motion, which ought to be in 
readiness ; and may even keep his object in view, as I have 
often done, by screwing the telescope backwards as fast as the 
round motion advances it. Then screwing himself forward 
again, he may repeat these successive motions as long as he 
pleases. 
In those observations, which I have called sweeps (from the 
method of oscillating or sweeping over an arch, which at first 
I had adopted in the way of right ascension, but which in the 
year 1783 I reduced to a systematical method of sweeping over 
zones of polar distance), several conveniences are required: 
the principal of them are as follows. 
An assistant, provided with an apparatus for writing down 
observations ; with catalogues of stars, atlasses, and other re- 
sources of that kind. 
A small apartment, as near to the observer as possible, in 
which this apparatus, with candles and other conveniences, 
may be inclosed. 
A sidereal time-piece. 
A right ascension apparatus. 
A polar distance apparatus. 
A polar distance clock. 
A zoned catalogue of the stars. 
And a ready communication between the observer and as- 
sistant, both ways. 
There is also wanting, a person to give the required mo- 
tions for sweeping the zones of the heavens. 
