996 Dr. Herschei/s Description of a 
a sweep. In the year 1783, when I began this kind of ob- 
servations, no catalogue of stars in zones had ever been pub- 
lished; I therefore gave a pattern to my indefatigable assistant, 
Carolina Herschel, who brought all the British catalogue 
into zones of one degree each, from the 45th degree of north 
polar distance down to the horizon, and reduced the right as- 
cension of the stars in it to time, in order to facilitate obser- 
vations by the clock. \ This catalogue was afterwards completed 
from the same degree up to the pole in zones of 5 degrees each ; 
and the variation in right ascension from one degree of change 
in longitude, was also reduced to time, for every star in the 
catalogue. To this were added computed tables for carrying 
back present observations to the time of that catalogue; which 
method I preferred to bringing the stars it contains forward 
to the present time, on account of conforming with the con- 
struction of the Atlas Coelestis, which was of great service. 
The evident use of such a catalogue must undoubtedly soon 
have been perceived by every person who was acquainted with 
the method I used for sweeping the heavens ; and as the same 
is practicable, not only with my telescopes, but likewise with 
transit instruments, and mural quadrants, we are now much 
indebted to the Rev. Mr. Wollaston, who in the year 1789 
favoured the astronomical world with a work of nearly a si- 
milar construction with that which I was in the habit of using; 
but much enlarged, and enriched with stars taken from the 
best authors; and moreover reduced to the time of the year 
1790. 
We now seem only to want an atlas on the same construc- 
tion, upon a scale equally extensive, and plentifully stored with 
well ascertained objects. 
