1887 .] C. Piazzi Smyth on the Edinhurgh Equatorial. 
13 
Also to exchange the present inefficient, yet cumbersome travel- 
ling and elevating platform and ladders, for a neat, compact, well 
seated and. suitably fitted Observer’s travelling hut, — freely tra- 
versing around, or to and from its generally proper and fully 
sheltered position at the end of the Declination axis, in any and 
every position of the telescope for observation arranged on the 
principles noted on the next page. 
And for Group No, 4, — he finally proposes to construct a new and 
grand Spectroscope with two sets of prisms (after the manner of that 
which he made for himself in 1882, and therewith discovered the 
exquisite spectral progression of Carbonic oxide, as well as the com- 
pound triples of pure Oxygen, in gas vacuum tubes) occupying in one 
plane and chiefly in a diagonal direction therein, all the hitherto 
unoccupied length between the upper or small-mirror end of the 
telescope tube, and the outer end of the Declination axis (as 
shortened) ; thereby balancing in itself, across the Polar axis, the 
heavy telescope tube, and its very heavy lower, or great-mirror, end ; 
and allowing an equivalent of dead weight to be taken off the 
Declination Axis. 
While he proposes also to utihse the whole length of the telescope, 
and the axial dark space necessarily running up through it as a 
Newtonian (or in this case a semi-Newtonian) reflector, — first in the 
part above the small diagonal mirror, for the objective of a large 
centrally placed finder to the telescope, always looking fully out of 
the opened shutter, whenever the telescope itself does (while it 
sends its cone of rays, by a diagonal mirror of its own, down to the 
end of the declination axis) ; and then below it, for the collection 
of rays for an end-on, gas-vacuum and electric lighted tube of 
his own invention, to form the reference spectrum for stars, in 
a manner more unexceptionable it is believed and more promising 
for accuracy than any aiTangement yet in use elsewhere. The 
observations being always as a rule, — and a rule most essential 
in the midst of a great and smoky city, growing greater and smokier 
day by day, — confined to as near the Meridian, and to as high 
an altitude therein, as possible. 
And now, as I believe that the above suggestions, worked out 
already to sufficient extent on paper, meet all the difficulties yet 
found with even superfluous force, I would try to call attention to 
