44 THE AMERICAN MONTHLY [Feb 
crometer screw. The stage has also a transverse microme- 
ter movement for the measurement of objects. The third 
microscope was made by John Cuff. The date of its in- 
troduction was 1744, and it was called “A New Con- 
structed Double Microscope.” After the John Marshall 
microscope this is historically one of the most important 
instruments in the Society’s collection. The other mi- 
croscope presented was made by Plossl and Cie, Wien. 
Messrs. R. and J. Beck exhibited a new pattern micro- 
scope embodying several new features. The substage 
was fitted with coarse and fine adjustments, and means 
of throwing out the condenser while it was in focus. The 
stage, 5in. diam., was rotating and graduated on the peri- 
phery, with a removable mechanical stage graduated asa 
finder. The body was very short, fitted with double-draw 
tube, which allowed the body to be extended to 11in. 
The body was fitted with Ashes’ new double-fine adjust- 
ment. 
Mr. Conrad Beck gave an exhibition of Anti-points, and 
said they were extremely difficult to show on account of 
the trouble there was in obtaining a light sufficiently 
smart and bright, and it was only possible to obtain faint 
images with so much diffused light as there was in that 
room. There was six microscopes, and all having fin. 
objectives, and the points of light in the first two cases 
were produced by minute apertures in tinfoil; in the 
others the light was reflected from small mercury glob- 
ules, With the first microscope a point of light was visi- 
ble with a 4in. objective of ordinary aperture, and shows 
a point of light surrounded with faint diffraction circles. 
With the second microscope a similar point of light was 
viewed with a din. objective of very small, aperture, and 
showed a disc of light and diffraction rings. The other 
microscopes showed the effects produced by placing vari- 
ous stops behind the objective, and also by viewing the 
point of light through a grating which extended the whole 
