267 
feature of which is the number of lines in the upper series 
is apparently doubled. Thus, an appearance of interpolated 
lines has been created by shutting out certain of the dif- 
fracted images, and an appearance of identity produced in 
objects known to differ, by the simple process of rendering 
their diffractive effects identical. 
Other experiments have been devised to illustrate the 
intimate connection between the diffraction of microscopic 
structure and their true appearance. The above, however, 
suffices to show the importance of using optical appliances 
constructed on principles founded on the recognition of the 
significance of the above facts. The dependence of the 
resolving power of objectives on their capacity to take in 
the diffracted rays, i.e., their “ numerical aperture,” is thus 
rendered manifest, and the value of the “ immersion ” prin- 
ciple in the constiuction of objectives of high power rendered 
specially prominent. 
The following is a list of Members and Associates, con- 
stituting the Natural History and Microscopical Section, on 
April 12th, 1886. 
Alcock, Thomas, M.D. 
Bailey, Charles, F.L.S. 
Barratt, Walter Edward. 
Barrow, John. 
Baxendell, Joseph, F.R.S. 
Bickiiam, Spencer II., Junr. 
Boyd, John. 
Brogden, Henry, F.G.S. 
Brothers, Alfred, F.R.A.S. 
Brown, Alfred, M.D. 
CoTTAM, Samuel, F.R.A.S. 
Coward, Edward. 
Coward, Thomas. 
CuNLiFFE, Robert Ellis. 
Dale, John, F.C.S. 
Darbishire, R. D., B.A., F.G.S. 
Dawkins, Prof. W. Boyd, M.A., 
F.R.S., F.G.S. 
Dent, Hastings Chas., F.L.S. 
Deane, W. K. 
Faraday, Frederick James, F.L.S. 
Hodgkinson, Alex., B.Sc., M.B. 
Hurst, Charles Herbert. 
Howorth, Henry Hoyle, F.S.A. 
Marsfiall, Prof. A, Milnes, M.A., 
M.D., D.Sc., F.R.S. 
Melvill, J. Cosmo, M.A., F.L.S. 
Moore, Samuel. 
Morgan, J. E., M.D., M.A. 
Nicholson, Francis, F.Z.S. 
Schwabe, Edmund Salis, B.A. 
Williamson, Prof. W. C., LL.D., 
F.R.S. 
Wright, William Cort, F.C.S. 
