NEW ROYAL OBSERVATORY, EDINBURGH. 
238 
declination wires, spectroscopes, solar eye-pieces with which the full 
aperture of the glass may be used with absolute safety, &c., &c. 
Immediately beneath the floor of the dome is another small chart-room. 
Opening from the platform to the south is, perhaps, the most 
interesting room in the whole observatory — the optical-room, measur- 
ing (36 feet from north to south by 24 feet in width. The zinc-covered 
roof is well shown in the photograph ; it is kept as low as possible to 
avoid obstructing the view of the heavens from the platform. This 
room can be completely darkened at a moment’s notice, while a pencil 
of rays fully ten inches in diameter, emanating from any celestial 
object — including the sun— can be thrown along the centre of the 
room by a Foucault siderostat on the platform. The rays enter 
the optical -room by a window in the northern wall. Into this window 
can be fitted, by self-adjusting contrivance, any of the object 
glasses belonging to the observatory. The images formed by these 
lenses can be examined by spectroscopes, eye- pieces, &e., mounted on 
massive iron tables capable of accurate adjustment. These tables run 
on one or other of four systems of rails carried by steel girders 
independent of the floor. Two pairs of rails are for the study of 
central rays, while the other two support apparatus for the reception 
of rays deflected by prisms on gratings. 
The ground floor of the building between the towers is taken up 
with a small spectroscope-room, laboratory, electrical -room, cleaning- 
room, mechanics’ workshop, and instrument-room; while in the eastern 
tower on the same level is a computing-room and a suite of photo- 
graphic rooms. 
On the ground floor towards the south, under the optical-room, 
are the director’s room, au auterooin, a computing-room, and the 
library. The latter is a fine apartment, 84 feet by 28 feet 9 inches, 
and being on a lower level than the rest of the rooms is sufficiently 
high to admit of a light gallery running round the wall. Here will 
be arranged the magnificent Crawford Library of astronomical and 
mathematical works, to which many recent presents and purchases, 
as well as many valuable works belonging to the Edinburgh Royal 
Observatory, have been added. 
In the basement are sundry store-rooms, a joiner’s workshop, the 
heating apparatus, and a large room for electrical batteries. 
The two equatorial instruments already mentioned are carried by 
massive brick piers built with cement. In the base of the larger of 
these is a small chamber, in which will be placed the two normal 
clocks of the observatory. The best of these was the gift to the 
Edinburgh Woyat Observatory of General Sir Thomas Makdougall 
Brisbane, whose memory is specially dear to scientific Australasians 
as the founder of the first observatory in Australia, and whose name 
is preserved in that of the flourishing city where your Association 
holds its meeting. The outer case of the clock bears the inscription, 
“ Sidereal governing clock, presented to R. Observatory, Edinburgh, 
by General Sir Thomas Makdougall Brisbane, Bart., 1855.” Thirty- 
nine years is but a short period in the life of a first-class astronomical 
clock, and, as far as can be judged, this masterpiece of Bent’s work- 
manship is still as good as when first received at the observatory. There 
is nothing special in its design, except that it has contact wheels on 
