4. “But such phenomena are not peculiar to microscopic vision, notwithstanding Professor Abbé’s claim to the contrary.
5. “With any positive lens similar and more brilliant results may be got by utilising corresponding pencils of primary rays, instead of isolated pencils of diffracted rays.
6. “Still more trustworthy results may be got by using primary rays in place of the isolated pencils of primary rays.
7. “An advantage peculiar to using narrow cone illumination with an objective of wide aperture (the only illumination admissible in the Abbé theory), consists in giving, under suitable conditions, approximately the acme of resolving power simultaneously in each several diameters. Thus a circular aperture is approximately squared or made rectangular as to resolving power in several of its diameters simultaneously.
8. “Special attention is called to the fact that the Abbé theory deals with complex objects; for only such objects are subject to resolution. Single particles and uniform areas are outside its domain. These latter, however, are microscopic objects, and all objects are essentially different shaped aggregations of points. An isolated point-like particle, no matter what its minuteness, may be seen if it present sufficient contrast with the surrounding microscopic field. The size of the disc image is no less than a limit determined finally by aperture. That limit in size varying inversely with aperture, determines the limit of resolving power. This is the gist of the theory of microscopic vision which harmonises with our experimental study of aperture.”
Appendix B.
MICRO-PHOTOGRAPHY.
Owing in some measure to the more complete knowledge of the subject gained by the experience of years, and the extreme value of micro-photography in the delineation of bacteria, and perhaps in a measure to the advent of the perfected dry-plate process, photography is being rapidly pressed forward in conjunction with the microscope. In the course of the year [1898] no less than six, more or less, new forms of micro-photographic apparatus have appeared; two are simple, one for daylight, one for lamp, one for electric, and one for lime-light illumination. Passing over the simpler forms, for a notice of which I am unable to find room, there is one piece of new apparatus, that of Mr. E. B. Stringer, which is not only new, but is in every way adapted to the work of micro-photography. It is in fact a well-arranged camera, fitted with a powerful condensing arrangement, each portion of which is capable of being independently centred and controlled. Indeed, the specially interesting feature of the apparatus is the control of the gas and the beautiful and uniformally illuminating disc of zircon, about a quarter of an inch in diameter.
Fig. 446.—Mr. E. B. Stringer’s Improved Micro-photography Apparatus.