On the Cork Equatorial Telescope, kc. 361 
The Roof of the Transit Room is segmental, concealed by a 
battlemented wall, and the shutter follows the same general 
form. Theshutter is all in one piece, about twenty feet long and 
two feet wide, and is supported at each end by two levers, which, 
linked together, form a parallel motion. (See Fig. 9.) These levers 
carry counterpoises at their lower ends, and the shafts on which 
these levers or parallel bars revolve pass across the Transit Room 
a few inches below the level of the wall plate, and to one of these 
shatts inside the building a lever is attached for opening and 
shutting. The shutter weighs about 5 ewt., but when perfectly 
balanced a weight of 2 Ibs. or a lever 3 feet long is sufficient to 
open or close it. In practice, however, it is found better not to 
have the shutter quite balanced, but to have a little overplus of 
weight tending to close it. A lock or bolt is also necessary other- 
wise the wind, even when very slight, is sufficient to open it. 
The shutter can be completely opened in two seconds. 
One good feature in this shutter is, that as in the latter portion 
of its journey the direction of its motion is nearly vertical, it 1s 
evident that it can be very efficiently flashed, i.¢., snow and rain 
guards can be applied of the most efficient construction. 
The Siderostatic Telescope (Fig. 10).—This instrument is unique 
+n its construction, so far as I know, but after having designed it 
for the Cork Observatory, I mentioned the principle of its con- 
struction to Dr. Draper, of New York, whose recent researches 
on the physical constitution of the sun have attracted such atten- 
tion; and it would appear that he has hit on the same idea, and 
was having one made in fact when he wrote to me. I have not 
as yet heard whether it is a success or not. 
This instrument, though obviously useful in many ways, 1s 
principally intended for solar spectroscopic investigation. It 
occurred to me that while in observing faint objects, such as 
nebule, faint companion stars, &c., observers are always most 
careful to keep their eyes protected from even the faintest light— 
that in observing the faint portion of the extreme end of the 
solar spectrum, observers are under the very worst possible condi- 
tions, for they must needs be in a room blazing with sunlight if 
they use a spectroscope attached to an ordinary equatorial 
mounting. I leave it to any observer to say what chance he 
would have of seeing faint objects in a telescope for ten minutes 
