PROCEEDINGS OF THE SOCIETY. 
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to the Jackson model of Microscope, and which were known to be 
superior. He referred particularly to Swift’s fine-adjustment as recently 
exhibited in the photomicrographic apparatus made for the Royal 
Veterinary College. In the original construction Messrs. Swift placed 
the coarse-adjustment in front of the fine-adjustment, so that the delicate 
bearings supported both ; but upon his pointing out that the mistake 
would really be equivalent to that of Zentmayer, Messrs. Swift at once 
altered the arrangement, making the fine-adjustment act by itself, and 
independently of the coarse-adjustment, so that the bearings had no 
other strain to endure than that involved in the motion of the fine- 
adjustment. It was clearly Dr. Van Heurck’s province to have known 
of this improvement in fine-adjustments already applied to the Jackson 
form of Microscope, and to have either adopted it or devised a new and 
better system. 
With reference to the application of a lever fine-adjustment to the 
substage, having the actuating milled head above the level of the object- 
stage, by which Dr. Van Heurck claimed that both fine-adjustments 
could be used simultaneously with one hand, Mr. Mayall said he con- 
sidered such an arrangement based on a total misapprehension of the 
essentials of practical microscopy. The position of the milled head was 
most inconvenient ; the observer’s fingers were liable to be caught by 
the stage mechanism ; it impeded the freedom of manipulation on the 
stage, and it stopped the rotation of the stage ; moreover, Dr. Van 
Heurck seemed to have overlooked the fact that the substage focusing 
motion was only brought into action in commencing an observation, and 
once being accurately adjusted was hardly touched again, unless for ex- 
perimental purposes. The focal adjustment of the objective was a 
totally different factor, demanding incessant manipulation in many high- 
power investigations. He could not imagine what possible motive 
Dr. Van Heurck could have in view when he claimed as a point of 
utility the faculty of using both fine-adjustments simultaneously. Fine- 
adjustments had long been applied to the substage. Mr. Nelson had 
had one carried out by Messrs. Powell and Lealand, by means of a cone- 
pointed screw and stud mechanism. He had had this arrangement applied 
to his own Microscope, and he regretted to have to confess his disappoint- 
ment with it, for it had introduced a new element of unsteadiness 
that was far more difficult to cope with than the former difficulty of 
focusing the condenser with the ordinary rack-and-pinion, which the 
fine-adjustment was intended to correct. A differential-screw mechanism 
had been applied by Mr. C. L. Curties, at the suggestion (he believed) 
of Mr. W. Lombardi, and this was embodied in Baker’s recently-made 
photomicrographic apparatus, which was exhibited at the Society’s Con- 
versazione in November last. Various forms of direct-action screw 
arrangements had been applied for the same purpose on the Continent. 
Hence, it could not properly be said that Dr. Van Heurck had 
discovered an important point hitherto neglected, and forthwith devised 
special and novel mechanism by which an essential improvement was 
effected in the Microscope as an instrument of research. 
The general design of the instrument seemed to have been copied 
from Bulloch’s Histological Microscope, and he was surprised that the 
single pillar support should have commended itself to any one in these 
