PROCEEDINGS OF THE SOCIETY. 141 



Archipelago. As in the case of those which preceded, it would be taken 

 as read, and published in the Journal. 



The JPresident said the Council bad, after careful consideration, 

 adopted some standard sizes for eye-pieces and substage fittings, par- 

 ticulars of which will be given in the Journal. The standard sizes were 

 the inside diameters of the tubes, into which the eye-pieces and substage 

 apparatus were to fit, and it would be left to the makers to determine 

 how tight or how loose the eye-pieces should fit into the tubes. Sets 

 of plug and ring gauges would be provided of these standard sizes, which 

 would be open to public inspection. No. 1 was that of the Continental 

 draw-tube. No. 2 was a larger size used by the Trade in England for 

 small Microscopes of inexpensive character, the Continental size being 

 found too small to give a sufficiently large field with low powers. No. 3 

 was the size which had given them the most trouble, as the sizes used in 

 the smaller-sized binocular Microscopes were so various ; but as these 

 were found to range from 1*2 in. to 1*35 in., the Council had taken 

 the mean between these sizes and adopted 1*27 in. No. 4 was the 

 largest size that a long-tube binocular Microscope could take. The 

 size of the eye-piece really determined the size of the Microscope, as 

 they would see by the examples upon the table before them, in which 

 the difference between the eye-pieces does not amount to two-tenths 

 of an inch. In coming to a decision on these questions the Council 

 had received very great assistance from the Trade, and they desired 

 to say how greatly obliged they felt for the information and help so 

 given. 



Dr. Spitta then gave a demonstration of some of the results obtained 

 by him in the course of his practical work in Photomicrography. In 

 his preliminary remarks he explained that the subject might be divided 

 into three sections : — low-power work, in which a Microscope cannot be 

 used, with powers ranging from 1^ to 10 diameters : medium-power 

 work, with the Microscope and powers from 10 to 6U0 diameters ; and 

 high-power work above 600, which was called critical photography. 

 The term " covering power " he fully explained, and showed its impor- 

 tance, especially with low powers. A remarkably fine series, consisting 

 of nearly 100 lantern slides, was then shown upon the screen, each being 

 accompanied by a brief description of the special points of interest in 

 connection with the subject, and the method or lens with which the 

 picture had been taken. The examples shown in illustration of work 

 with quite low powers comprised insects, spiders, plant sections, echinus 

 spines, &c, some of which were taken in duplicate to show the com- 

 parative merits and different objectives employed — those pictures pro- 

 duced by the planar being conspicuously fine. Under medium -power 

 work some excellent photographs were also shown of 2>ortion8 of 

 insects ; lancets and other mouth-organs being amongst the best of the 

 series. How to photograph thick specimens was explained, the sections 

 of kidney and of nerves being extremely well shown ; but perhaps the 

 greatest interest was shown in some unique views of Filariae in the 

 blood-vessels of the human lungs, and in the bodies of the mosquitoes 



