im 
Mr Waddell on a New Optical Instrument. 
Directors of the Highland Society, they expressed their willing- 
ness to co-operate, and appointed a Committee to confer with a 
Committee of the Wernerian Society on the business ; and it is 
in contemplation to communicate with the Right Honourable 
the Earl of Dalhousie (a Vice-President of the Society, and now 
Governor-General of Canada), and request the good offices of 
that patriotic nobleman towards the sending home of living spe- 
cimens of the animal. 
Art. XXII. — Account of a New Optical Instrument , winch 
combines the properties of a Compound Microscope , Camera 
Ohscura , Camera Lucida, and Diagonal Mirror. By Alex- 
ander Waddell, Esq. 
My Dear Sir, 
Since I furnished you with a drawing and description of an 
optical instrument I constructed about eight years since, which 
you inserted under the Article Microscope of the Edinburgh 
Encyclopedia , I have lately adopted a different mode in the 
construction and application of it, which, I think, combines cer- 
tain advantages that the former did not possess. I therefore 
send you a drawing and description of it, lest you may think 
them worthy of a place in the Edinburgh Philosophical Jour- 
nal. 
Fig. 3. of Plate IV. represents the instrument under its im- 
proved construction. The body is formed of two hollow hemi- 
spheres of brass screwed together, within which is placed a me- 
tallic reflector, at an angle of 45° with the tubes of the instru- 
ment, which are screwed into the upper and front sides of the 
hollow ball of brass, the diameter of which is about four inches. 
The instrument is represented fitted with a right-angled trian- 
gular prism, placed at the outer end of the horizontal tube or 
tubes, in order to correct the position of the objects which, al- 
though erect when viewed without it, would otherwise be re- 
versed. The object-glass of this instrument is formed of two 
lenses, each of double the focal distance required, placed at the 
points where the tubes are fixed on the top and front of the 
ball ; and the eye-piece is of the usual construction in telescopes, 
and has a compound eye-glass. 
