78 
Transactions of the Royal Microscopical Society. 
III . — Note on a New Paraboloid Illuminator for use beneath the 
Microscope Stage. Also Note on the Resolution of Podura 
Scale by means of the New Paraboloid. 
By James Edmunds, M.D., M.R.C.P. Bond., &c. 
( Taken as read before the Royal Microscopical Society.) 
The glass paraboloid, known as Mr. Wenliams, is so useful an 
accessory that no microscope is complete without it ; and, for dark- 
ground illumination, with dry-front objectives up to a considerable 
angle of aperture, the results are excellent. But with high powers 
of large angular aperture and with immersion fronts, the Wenham 
paraboloid introduces fog, while it fails to give a dark back- 
ground. That these radical defects are inseparable, not merely 
from the Wenham paraboloid, but also from all our present con- 
trivances for oblique sub-stage illumination, will be obvious to 
everyone on considering the following diagram. 
Assuming that, by means of Wenham’s paraboloid, a long 
focus objective, or other contrivance, a pencil of light be success- 
fully thrown upon the under surface of the slide at an angle of GO 3 
