1892.] on Optical Projection. 537 



ments with polarized light. I will show on the screen a diagram of 

 the polariscope. (Shown.) 



With reference to showing the spectrum. The method of pro- 

 jecting a spectrum, I think, is new, as I have not seen it described 

 anywhere. It gives practically a direct spectrum with an ordinary 

 prism, without turning the lantern round to an angle with the 

 screen ; and here is a diagram of the method. 



The details of the apparatus, as well as those of the methods of 

 working, I have modified in almost every instance, for five reasons : — 

 (1) That more certain results may be ensured ; (2) that rapidity may 

 be obtained ; (3) that only one operator may be needed ; (4) that, as 

 far as possible, all parts of the apparatus may be interchangeable 

 and (5) that loose screws and pieces may be dispensed with. 



There were then shown by projection a number of slides illustrat- 

 ing various microscopic optical systems, and a number of microscopic 

 slides, followed by a series of general polariscopic projections, some 

 of them to illustrate the strains existing in many forms of matter ; 

 also a spectrum by a carbon disulphide prism, in conjunction with a 

 reflecting prism and with a mirror, which, apart from any other 

 result, demonstrates that the loss of light with a reflecting prism is 

 less than with an ordinary glass mirror. Slides and other projections 

 were also thrown upon the screen. 



The details are as follows : — 



The Microscope. — Screen distance, 21 feet. First, 35 millimetres 

 Zeiss projection objective, 4-inch sub- stage condenser, Zeiss Huyghens 

 eye-piece 2 ; 500 diameters = 250,000 times = penny stamp stretched 

 to cover about 147 square yards. Subjects shown : proboscis of blow- 

 fly ; permanent molar displacing milk-tooth (kitten) ; human scalp, 

 vertical ; human scalp, surface ; fossil ammonites and |belemnite. 

 Second, 1-inch Newton's projection objective, 4-inch sub-stage con- 

 denser, Zeiss Huyghens eye-piece 2; 1000 diameters = 1,000,000 

 times = stamp stretched to about 588 square yards. Objects shown : 

 proboscis of blow-fly ; foot of a caterpillar ; section of human skin, 

 showing the sweat ducts ; phylloxera vastatrix of the vine. Third, 

 1 inch Newton's projection objective, 4-inch sub-stage condenser, 

 Zeiss Huyghens eye-piece 3 ; 1300 diameters = 1,690,000 times = 

 stamp stretched to about one-fifth of an acre. Slides shown : proboscis 

 of blow-fly ; wings of bee (showing booklets and ridge) ; sting of bee 

 (showing the two stings, sheath, and poison-sack) ; sting of wasp 

 (showing same as last slide) ; eye of beetle (showing the facets). 

 Fourth, i-iuch Zeiss's achromatic objective ; Abbe's 3-lens sub-stage 

 condenser, with top lens removed ; Zeiss Huyghens eye-piece 3 ; 

 4500 diameters = 20,250,000 times = stamp extended to nearly 2^ 

 acres. Slides shown, proboscis of blow-fly ; hair of reindeer (showing 

 cell structure) ; hair of Indian bat (showing the peculiar funnel-like 

 structure) ; sting of bee (showing the barbs) ; foot of spider ; stage of 

 the micrometer (the closest lines ruled to thousandths of an inch, which 



Vol. XIII. (No. 86.) 2 o 



