556 
PROCEEDINGS OF THE SOCIETY. 
regrettable from the fact that so few microscopists in England had their 
pliotomicrographic apparatus installed for use with sunlight. The diffi- 
culties involved in obtaining suitable objects for examination with Zeiss’s 
new objectives of 1*6 N.A. were very great, due, as he understood, to the 
chemical action of the dense mounting medium on the flint-glass covers. 
So far the Society had not received a slide of a kind that could be 
regarded as satisfactory for testing such an objective. 
Mr. C. L. Curties exhibited in its finished form Mr. Nelson’s 
apparatus for obtaining monochromatic light, a specimen of Bhomboides 
being shown under a dry 1/6-in. objective. 
Mr. Mayall said Mr. Curties had had the apparatus made entirely of 
metal, and had hit upon an inexpensive design, though the construction 
seemed rather too light to be steady enough for general use. He 
thought there was no absolute necessity to employ a high-class photo- 
graphic lens for projecting the spectrum ; any moderately good achromatic 
lens of suitable focus would answer the purpose. He understood from 
Mr. Nelson that for observation work with the Microscope the optical 
combination at the lantern or slit end of the apparatus was not needed, 
the slit screen being sufficient ; but for photomicrography, by means of 
artificial light, this optical combination was important to increase the 
light. The apparatus was so devised that the microscopist might employ 
any prisms or photographic lenses he possessed. He thought the pierced 
cardboard on which the spectrum was projected would soon warp out of 
shape, and that it might be replaced with advantage by a metal plate 
coated white, which would retain its shape. If a prism had to be made 
specially, one of light crown-glass would probably answer better than 
the dense flint. 
Mr. T. T. Johnson exhibited and described a new form of student’s 
Microscope which he had devised. 
Mr. Mayall said the special point was in the application of a screw 
movement instead of the usual rack-and-pinion to raise and lower the 
substage, the screw being in the axis of the bearings of the substage and 
tail-piece, and the actuating milled head projecting slightly at the back 
of the stage. He thought this was a very economical way of applying 
focusing mechanism to the substage. The position of the actuating 
milled head seemed to him most happily chosen for convenience, though 
it would probably be necessary to make the head larger so as to provide 
more grip for the finger, as the movement would be certain to become 
less free in course of time. When he saw the instrument on the previous 
da} 7 he pointed out that the mirror was connected with the substage and 
went up and down with it ; this defect had since been corrected. He 
thought this substage adjustment would commend itself to notice, and 
that if it was not already registered it would certainly be taken up by 
other opticians for the less expensive forms of Microscopes. It seemed 
to him that Messrs. Johnson had undoubtedly “ scored I ” by bringing 
out this screw-focusing arrangement for the substage. 
Mr. W. Johnson said the arrangement had been devised by his son 
with very small encouragement from himself. He had to thank Mr. 
Mayall for calling his attention to the mistake of connecting the mirror 
