Shutters for a Dome for an Equatorial Telescope. 375 
advisable. 
By these methods the heights of many thousand points have 
been determined, from which to construct a map in “ contours” 
200 vertical feet apart, on a scale of two miles to one inch. 
olorado Territory is the greatest center of elevation known 
on the continent; and it is the intention of the Survey to have 
its maps render with accuracy the general form and sculptured 
features of the great and varied mountain ranges, whose won- 
derful structure will be a subject of investigation to the geolo- 
gist for years to come. 
Arr. XLIL.—On a New Arrangement of Shutters for a Dome for 
an Equatorial Telescope; by EpwARD S. HOLDEN. 
Iv the mounting of equatorial telescopes, particularly those 
of large size, much difficulty has been met with in providing 
suitable shutters for closing the openings in the dome through 
which the observations are to be made. 
The conditions to be fulfilled in the slit and shutters are 
mainly as follows: 
currents of air near its edges, without much disturbance near 
man with ease. They must be waterproof; they must not be 
liable to get out of order. It should be necessary to lift as little 
Weight as possible; if practicable, the whole of the slit should 
be uncovered at once. Various styles of covering for large tel- 
€scopes have been contrived, in the endeavor to fulfill these 
are: 
st. The sliding roof, like that of the Cincinnati Observatory. 
u 
Point, Washington, and other places. It is probable that the 
Sliding roof will not be used for the largest class of instruments. 
