92 Sir J. Herschel’s Astronomical Observations 
the Professor who had lent him the use of the telescope. In 
the course of the following year, in conjunction with his class- 
mate, Mr. Hamilton Smith, he constructed a fourteen-feet reflect- 
or, having an aperture of twelve- inches, which was at that time 
the largest instrument of the kind in the United States. For- 
midable as this undertaking was, these two enthusiastic young 
m 
of perfection ; having, with their own hands, cast the great spec- 
ulum, given it the requisite figure, and imparted to it its final pol- 
ish. In fact, ac a little occasional aid from ordinary mechan- 
ics, they may be said to have made all the other parts of the in- 
strument cicshinn the tube and the stand. It was an excellent 
instrument, in most respects, but more especially for the fine light 
elass, in the summer of 1839, being now released from the ordi- 
nary routine of college duties, our youthful astronomers com- 
menced the laborious observations after which they had so eagerly 
panted. ‘These were prosecuted during the following year by 
Mason alone, along with numerous micrometrical esartgsicee taken 
with the Clark telescope belonging to Yale College. 
In the article on the Nebule afterwards published by Mewes 
in the American Philosophical Transactions, he says respecting 
their peculiar method of observation, “It consists not in an ex- 
tensive review, but in confining the attention toa few individ- 
uals ; upon these exercising along and minute scrutiny, during 
a succession of evenings; rendering even the slightest particulars 
of each nebula as precise as repeated observations, and compari- 
son with varied precautions, can make them, and confirming each 
more doubtful and less legible of its features by a repetition of 
suspicions, which are of weight in proportion as they accumulate ; 
and, lastly, when practicable, correcting by oe ot the 
judgments of different persons at the same tim oo 
In the delineation of the objects thus carefully observed, Mason 
adopted also a process of his own invention. _ It is sufficient to say 
that in delicacy and beauty, his figures are but little inferior to 
those of the work before us. For their accuracy, we have the 
suapenisy of Sir John Herschel himself. The nebule selected 
for observation by Mason were from the catalogue of Sir John, 
published in the Philosophical Transactions for 1833, and were 
four in number, (A. 1991, 2008, 2092, 2093.) They proved, 
however, to be actually but three, for the last two of the series 
they disco 
vered to be one and the same sunset wai ea 
* 
