Mr. Pond on the changes which have taken place , &c. 35 
decide with certainty, that which otherwise would become an 
endless subject of doubt and conjecture. 
I had often attempted to observe the altitudes of stars by 
means of an artificial horizon of quicksilver, or other fluid, 
but had abandoned the attempt from the difficulty of pro- 
tecting it from the wind, and from the number of observa- 
tions I lost in fruitless experiments. To this method I had 
again recourse ; and by means of wooden boxes of different 
sizes and figures, according to the different altitudes of the 
stars, I have sufficiently accomplished my purpose. A very 
few observations were sufficient to convince me that the in- 
strument was in every respect perfect, and that I might repose 
the greatest confidence in every result it gave. 
Several stars, and particularly those most discordant, I 
have observed by this new method, and find their places, 
without any exception, to agree within a fraction of a second, 
with those determined by direct measurement from the 
pole. 
Presuming that the observations* which accompany this 
paper will remove every shadow of a doubt as to the accu- 
racy of the instrument, I shall now proceed to state, in as 
few words as possible, the nature of the changes which ap- 
pear to me to have taken place since the year 1812. 
If Bradley’s catalogue of stars for the year 1756, be com- 
pared with the Greenwich catalogue for 1813, it will be pos- 
sible to deduce the annual variation for each star for the 
mean period, or for the year 1784, on the supposition of uni- 
formity in the proper motion of each star ; then allowing 
for the change of precession for each star, a catalogue may 
* Vide Appendix. 
