1864.] 
and yet at the same time a uniform 
curve and absence of local irregulari- 
ties secured. I have spent five 
years in the investigation of this 
subject, and have polished more 
than 100 mirrors of from 19 inches 
to one-fourth of an inch in diameter, 
on seven different machines built 
at various times. The quality of 
those I have at present is indi- 
cated by the fact that they will 
show Debillisima to be quintuple, 
and will render the close companion 
of Sirius, discovered by Alvan 
Clark’s magnificent 18-inch refrac- 
tor, visible. 
The Observatory at Hastings- 
upon-Hudson, near New York, lat. 
40° 59! 25” N., long. 73° 52/ 25" W. 
of Greenwich, is upon the summit 
Notes and Correspondence. 
383 
of a hill 225 feet above low-water 
mark. It is 20 feet square, with a 
wing 9x10 for a photographic 
laboratory. As the telescope is a 
Newtonian, with the mounting so 
contrived as to have the eyepiece 
stationary at all altitudes, a plan 
originally suggested by Miss Her- 
schel, there are peculiar facilities 
offered for easy access to the eye- 
piece, or place of the sensitive plate. 
The interior height of the Observa- 
tory, 22 feet, is divided into two 
stories, around the upper of which 
an observer’s chair runs to follow 
the telescope. The dome turns upon 
a pivot at its centre, instead of on 
rollers or cannon-balls around the 
edge, and is moved consequently 
with but slight exertion. 
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