ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
95 
in any other form. For instance, in our Edinburgh Student’s Micro- 
scope — a section of a limb of which is shown in fig. 3 — the total length 
of the lever arms is 2 T \r in., the arm on the one side being 3/8 in. long, 
and on the other 1-J-J- in. The weight of the body, fittings, &c., is 17 oz. 
The resistance at the end of the lever is therefore 3^ oz. We have not 
included the reactionary spring in these figures, as this is employed in 
all forms of fine-adjustment, but the resistance of this is minimized at 
the point of force, in the same ratio as the weight. Also by means of 
the long lever an extremely slow motion is obtained, the movement being 
lessened in the same proportion as the weight. 
All fine-adjustments must wear in course of time as the result of 
friction, and in the majority of cases it is irremediable, except in the 
maker’s or a skilled mechanic’s hands. In our form the fitting is sprung 
and has two screws (shown in fig. 4, A), by means of which any wear 
as the result of friction can be at once taken up by the user. This is 
of the greatest importance to residents abroad, the necessity of returning 
an instrument to be adjusted being obviated. 
The coarse-adjustment fitted to our instruments is as shown in 
fig. 4, and is effected by means of a diagonal rack and spiral pinion, 
which ensures the smoothest possible motion and an entire absence of 
backlash, the teeth of the pinion never leaving the rack. High powers 
can be exactly focused by its means without the aid of the fine-adjust- 
ment. This adjustment and all the frictional parts of the instruments 
are fitted with screws, as in the fine-adjustment, which by being very 
slightly turned compensate for wear and tear.” 
Note on Watson’s Edinburgh Student’s Microscope. — Mr. E. M. 
Nelson read the following note at the November meeting : — “ It will be 
remembered that a certain amount of controversy was raised with regard 
to a Microscope exhibited here by Messrs. Watson and Sons last year.* 
I am now alluding not to the general design of that instrument, but solely 
to the fine-adjustment. Whatever the general design of an instrument, 
or however simple or complex its movements may be, its real value for 
work entirely stands or falls with the quality of its fine-adjustment. 
It is well to remember the axiom propounded by the late T. Powell, 
‘ that a Microscope without a fine-adjustment, but with a good coarse- 
adjustment, is to be preferred to one, however elaborate, with a bad fine- 
adj ustment.’ 
The question in dispute, therefore, is of supreme importance. At 
that time my opinion with regard to the fine-adjustment was asked, but, 
never having seen it, it was impossible for me to express any opinion on 
the subject. Since then Messrs. Watson and Sons wrote to me, saying 
that they were confident of the soundness of the principle of their fine- 
adjustment, and that if I would examine one, they would submit an 
instrument for my prolonged investigation. To this I agreed, and I am 
now in a position to answer the question asked last year regarding this 
fine-adjustment. 
The adverse critics said that this fine-adjustment was on the Zent- 
mayer plan, and as the Zentmayer fine-adjustment was a miserable 
failure, this one must be a failure also. This might have been very 
* This Journal, 1891, p. 434. 
