560 
PROCEEDINGS OF THE SOCIETY. 
allows of the use of Continental as well as English objectives ; its price 
is less than the large Continental stands; and, lastly, I challenge 
Mr. Mayall to make, with any Microscope he chooses, a delicate observa- 
tion or any photograph which I cannot just as easily, conveniently, and 
perfectly make with my instrument.” 
Mr. Mayall said, with reference to Dr. Van Heurck’s communication, 
there appeared to be only one matter calling for a detailed reply from 
him, and that was the oblique thrust given by Dr. Van Heurck in stating 
that the Mayall mechanical stage was nothing but the Wenham stage 
of 1878 rendered independent of the Microscope-stage. In assisting 
Mr. Frank Crisp in the preparation of the illustrated and descriptive 
catalogue of his Microscopes, &c., examples of nearly every Microscope 
and piece of accessory apparatus known had passed through his hands, 
and he had not only examined them all with considerable attention, but 
liad taken many of them to pieces in order the better to understand and 
describe the mechanism. He thought, therefore, it might reasonably be 
supposed that if Mr. Wenham had preceded him in embodying the 
principle of the Mayall stage, the fact would not have escaped his own 
notice. Further, he might say that when he decided to have his stage 
made he went to Ross & Co., in whose house Mr. Wenham was engaged, 
and assuredly Mr. Wenham would at once have pointed out that the stage 
was a plagiarism if such had been the case. The fact was that Dr. Van 
Heurck had made a random guess at the matter without special know- 
ledge, and had missed the point. In the course of years there had been 
a process of evolution going on in mechanical stages as in other parts of 
the Microscope. At first they were very elaborately made by the Due 
de Chaulnes and by B. Martin in the last century, and were far ahead of 
the optical appliances to be used with them ; then they were simplified, 
and brought into more general use ; then, with the general introduction 
of achromatism, altogether superior mechanism was employed, and so 
important was it found to secure steadiness of motion, that stages were 
made of considerable thickness. Later on, attempts were made to reduce 
the thickness, and Mr. Wenham devised a stage using one plate only to 
carry the object. Mr. Tolies, the eminent optician of Boston, sent over 
a beautifully made stage, having two plates each of about 1/50 in. 
thick, which Mr. Wenham modified by getting rid of one of the plates ; 
and later still, he (Mr. Mayall) suggested that the plate might be 
removed and a frame substituted, by which the object could be moved 
about on the surface of the stage proper of the Microscope. The idea 
was found practicable and was taken up by various opticians, most 
recently by Zeiss, of Jena. So far, therefore, as regarded Dr. Yan 
Heurck’s imputation that he had plagiarized Mr. Wenham’s stage of 
1878, he could only regard that oblique thrust as, in fencing phrase, a 
“ coup de Jarnnc,” and he did not feel under any sort of obligation to 
acknowledge that he was “ hit.” His remarks at the last meeting were 
intended to apply only to Dr. Van Heurck’s specification and from what 
he then said he did not abate a word. He thought much of Dr. Yan 
Heurck’s defence of the Microscope was actuated by his not distinguishing 
between the design and the actual construction. On several points too, 
Dr. Yan Heurck appeared not to have followed the criticism. He must add 
that the instrument itself had since been in his hands for trial, and he 
