538 
PROCEEDINGS OF THE SOCIETY. 
accomplished by means of some small wheels which traversed the outer 
edges of the horse-shoe plate, the transverse movement being given to 
the slide itself by means of the rotation of other wheels caused to clip 
it upon either edge by the pressure of a spring. Motion was imparted to 
the wheels by the rotation of a milled head to each set which acted 
upon an endless screw. By means of diagrams Dr. Dallinger was able 
very lucidly to explain the mechanical details of this extremely ingeni- 
ous and novel design, which he further stated could be produced at about 
one-half the cost of the Mayall stage, which was perhaps the best 
reliable form previously introduced. 
The Chairman said they were greatly indebted to Dr. Dallinger for 
the description of this new stage, which no doubt had been followed by 
all with great interest. 
Mr. T. Comber said he had been examining the details of this very 
admirable contrivance before the meeting began, and it occurred to him, 
that excellent as it was, there was one improvement which could be made 
in it. He noticed that the milled heads which turned the wheels were 
placed one on one side of the stage and the other at the opposite side, 
so that both hands would be required to work it ; this, he thought, would 
be rather inconvenient. If, however, both these were on the same side, 
they could be managed by one hand, leaving the other free to work the 
focusing arrangement ; this appeared to him to be a practical improve- 
ment which he thought it would be possible to carry out. 
Mr. J. Swift said that this improvement had already been suggested 
by Mr. Karop, and there would be no difficulty in carrying it out. 
Dr. Dallinger said he desired rather to abate criticism upon a thing 
which he was so thankful to get, feeling that it would be a great pity to 
sacrifice the instrument for the sake of some ideal improvement, but he 
might perhaps mention that the idea of Mr. Nelson in having the horse- 
shoe stage was that the fingers might have free access to that part which 
the arm in front seemed to close against them. 
Mr. J. More, jun., thought the success of the whole thing depended 
upon the accuracy of the edges of the slide ; if these were parallel, of 
course it would work, but very often the slides were not so true, and 
this would prevent it from acting. 
Dr. Dallinger thought the non-parallelism of the slide would affect 
the working very slightly by causing the movement across the field to 
be at a small angle of inclination, but the spring would be quite suffi- 
cient to keep the wheels in good contact with the slide even if its edges 
were considerably out of parallel. 
Mr. C. Beck thought the idea was extremely ingenious, and that 
Mr. Swift was much to be complimented upon the successful way in 
which it had been carried out, because it was certainly new in design, 
and seemed far more likely to be useful than some other contrivances 
they had seen for the same purpose. He noticed that, to prevent any 
tendency for the slide to rise from its plane, the wheels were slightly 
bevelled down. The question as to whether the slide moved in 
straight lines or not, was one which made no difference for practical 
purposes. 
