PROCEEDINGS OF THE SOCIETY. 
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Mr. Mayall, that I have a totally wrong idea of the essential principles 
of practical microscopy. — I regret I cannot accept Mr. May all’s decision. 
I have my own method of working, a method too long to be described in 
this letter, and as this method enables me to produce work which is said 
not to be wholly valueless, I shall persevere in my errors. (3) Mr. 
Mayall says that the milled head of the fine-adjustment of the substage 
prevents the full rotation of the stage. — Here it is Mr. Mayall who 
seems to misunderstand the use of this rotating movement. We are no 
longer in the time when the illuminating apparatus consisted of a simple 
mirror, and the complete rotation might be of some utility. The con- 
denser really is so arranged as to permit of a luminous pencil being 
moved all round the object. The rotation is therefore no longer necessary, 
except for adjusting the object in a convenient position for drawing or 
photography, or according to the astigmatism of the observer’s eye. For 
all these purposes, the movement which the stage of my instrument 
possesses is more than sufficient. (4) Mr. Mayall criticizes as wrong 
the size of the milled heads of the movements of the stage. — It is, how- 
ever, an elementary principle in mechanics that the larger the lever 
used, the better it will effect small, easy, and precise movements. If 
Mr. Mayall had tried oftener to put a diatom in the best possible position, 
either for photography or to make one of its striae correspond with the 
micrometer, he would not recommend the small milled heads of the 
Mayall-Zeiss stage. This latter, with which I have worked for some 
time, can be used for finding an object, but it is very tiring to the fingers 
for continuous work, and cannot be used for work of precision. The 
displacement produced by the least motion of the milled head is far too 
rapid. (5) I am in the habit of photographing in the vertical position, 
and if one pillar gives me a sufficient stability, I do not see why I should 
have a second one, which would only hinder the handling of the mirror 
and parts of the substage. A second pillar only adds to the stability 
when it is put at a considerable distance from the other, as Messrs. 
Powell and Lealand make it. (6) The centering of the substage, de- 
scribed as of a cheap kind by Mr. Mayall, completely answers its 
purpose. It is the same as is used for the centering of the stage in 
Wenham’s radial and Zeiss’s Microscopes, &c. It would have been 
quite useless to spend money in superfluous complications. (7) The 
small screw to clamp the Microscope in the horizontal position was 
added by Messrs. Watson of their own accord. As I use only vertical 
cameras, I did not require it. It is possible that they took the idea 
from one of Swift’s Microscopes ; this, however, does not matter. The 
Mayall stage is nothing but Wenham’s, constructed about 1878, but 
rendered independent of the Microscope-stage. No apparatus is now 
constructed, the suggestion of which cannot be found in some former 
Microscope. I believe I have replied to all the points criticized by 
Mr. Mayall. None of them seem to stand, and as for over two years I 
have used a similar instrument (which I had modified according to my 
experience) for my most delicate researches with the best results, I 
thought that others might use it with the same advantages. But one 
must not forget the conditions I prescribed : combine the convenience 
for everyday work with the greatest precision possible, at a relatively 
low price. I now maintain that the instrument fills these conditions ; it 
