128 SUMMARY OF CURRENT RESEARCHES RELATING TO 



we should be able to sec a similar objoct or objects if tbcy could be 

 presented to our unaided vision, of tlie same size as the microscopic 

 images, at the ordinary visual distance, and mounted in equivalent 

 dci^tbs and tliicknesses of mounting material. In sliort, that we 

 see the objects suspended, as it were, in tlieir true relative posi- 

 tions to cacb otber in the mounting medium, those nearest to 

 the eyes or lying in the plane to which the focus has been most 

 perfectly adjusted being, of course, best defined, whilst those situated 

 below or above that plane are seen very nearly, if not quite, as dis- 

 tinctly as they would be in ordinary vision were the conditions assi- 

 milated to the extent already indicated. Of course, I do not assert 

 that any condenser can impart to any objective additional 2:)enetrative 

 power to that already implanted in it. What I claim is that the new 

 mode of illumination su^jplies those conditions which allow any 

 objective to ' jiut its best leg foremost.' 



In the second place, I claim that this method of illumination 

 proves that there are such things in microscojiic vision as ortlwstereu- 

 scoplc projection and perspective." Dr. Wallich then goes to say that 

 tlie existence of both of these " attributes has, as we all know, been 

 " emi)hatically and unconditionally denied by more than one of our 

 " most accomplished and deservedly renowned theoretical opticians." 

 Dr. Wallich, however, in making this statement, has misappre- 

 hended the views to which he refers, which are not in conflict, as he 

 supposes, with any results obtained by him.* The further state- 

 ment that " Dr. Carpenter has for many years stood alone in con- 

 tending that true stereoscoj)ic vision does not take place in the 

 Microscope," contains, we presume, a misprint, in that the " not " 

 should have been omitted. 



Osborne's Diatomescope. Modified Wenham Disk Illuminator.f — 

 W. F., whilst having no doubt that the diatomescope will give a pencil 

 of light sufficiently oblique for the various ol)jectives used, considers 

 that the same result can be got in a much simpler and cheaper way. Mr. 

 Wenham's disk illuminator serves the object in view very well ; but 

 it has one serious defect — there is no provision for a shutter in front 

 to narrow the band of light. He prefers to take a hemispherical lens 

 about 1/4 or 3/8 in. in diameter, and after burnishing it into a setting, 

 cut the setting almost entirely away at one side, leaving only sufficient 

 to hold the lens. Slip this lens so mounted into the top of a tube of 

 the proper size, and slit the tube at one side below the lens down- 

 wards for 1/2 in. or so with a fine saw. The cut sides of the tube 

 chemically blacken. When the tube is mounted beneath the stages 

 so as to almost touch the object slide, and with a provision for 

 turning it slightly round, the lamp being placed in front of the slit 

 in the tube, it will be seen that the band of light transmitted by the 

 lens may be made any breadth from the width of the cut in the tube 



* See this Journal, iv. (188i) jip. 49G-7. 

 t Engl. Mecli., xl. (lSS-1) p. 321. 



