130 EH. & Holden—Light of Telescopes used as Night-glasses. 
for the Insane, which is 20,798 feet distant from the center of 
the Dome* 1” at this distance is 13 inches; 1’ is 78 inches. 
The accompanying figure will give the best idea of the 
object viewed. ‘The drawing has been kindly made for me by 
Shipman, Esq., of Chicago. I have marked upon the 
cut the line of the horizon, from sic it appears that the 
10 6. 
Diam.66 000 eS Me cee ae s 
Sto 
_ ao" 5 
EF | 
= 
F G ee 
teri d 
22 6 
es 
I Ps 
| 980" = 
a0 
saa abit ae 
H H 
whole tower has an elevation of about 9’ above the horizon 
line, In the observations which follow, the part A B, (10 feet 
high), is spoken of as ‘the spire;” B G, (9 feet), as “the base 
. the spire ;” the next section, (13 feet high), as “ the cupola” 
“the dome,” and the remaining portion, as “the tower.’ 
he 2 finder has an aperture of 3°50 inches, a field of 1° 20%, 
and a magnifying power of 26 diameters. The refractor has 
an ay of 15°56 inches, a field of 11’-6, and a power of 199 
iamete 
The following thee ea were made 1881, April 18, by 
Mr. 8. urnham and m 
The whole sky was pertectly eles except a very faint bank 
of clouds to the west of the tower looked at. The observations 
were as follows: Hn. standing for observations made by 
Holden ; for those made by Burnham 
* T have to express my thanks to Professor J. E. Davies for the sci cuitasiik 
tion of the Coast Survey data re atte these figures are derive 
