"oum!?;, jinfi^Tsm'] «s applied to PJwto-mierography. 299 



from the 6th square of a Moller's diatom type-plate, specially 

 prepared for the Army Medical Museum by that skilful micro- 

 scopist. The first, from Negative 79 (new series), was taken by 

 sunlight, with 40 diameters ; in the second, from Negative 123 

 (new series), the Magnesium light was used, and everything else 

 remaining the same, the distance was increased so as to give 48 

 diameters; in the third, Negative 158 (new series), the Electric 

 lamp was employed, and everything else still remaining unaltered, 

 the distance was increased so as to give 66 diameters. It will be 

 understood at once, that on account of the increase of distance, the 

 second picture would have been slightly less sharp than the first, 

 and the third than the second, had precisely the same source of 

 light been employed ; nevertheless, in spite of this disadvantage, to 

 which they were purposely exposed, the Magnesium and Electric 

 pictures are far superior to that taken by sunlight, and of the two 

 the Electric is much the best. It is especially to be observed, that 

 in the Electric picture the contrast obtained is so great that the 

 objects appear clearly defined on an almost perfectly white ground, 

 which is never the case with Photo-micrographs taken with the sun 

 as a source of illumination. 



As a further illustration of the capabilities of the Magnesium 

 and Electric lights, I add a few photographs taken by each. 

 [Specimens of all these are now, owing to the courtesy of Dr. 

 Woodward, in the possession of the Royal Microscopical Society.] 



By the Magnesium Light. 



Arachnoidiscus Ehrenhergii. Magnified 400 diameters, by 

 Wales' |th. Negative 114 (new series). 



Smcdl vein and capillaries, from the muscular coat of the 

 urinary bladder of the frog. Magnified 400 diameters, by Wales' Jth. 

 Negative 103 (new series). This negative is taken from pre- 

 paration No. 3378, Microscopical Series, in which the bladder was 

 injected with a half per cent, solution of nitrate of silver, and sub- 

 sequently stained with carmine dissolved in borax. The epithehum 

 was then brushed ofi" with a camel's-hair pencil, and the preparation 

 transferred through absolute alcohol to Canada balsam ; the photo- 

 graph reproduces everything but the colour. 



By the Electric Light. 



Pkurostaurum acuium. Magnified 340 diameters, by Wales' 

 ^th. Negative 109 (new series). 



Triceratium favus. Magnified 340 diameters, by Wales' |-th. 

 Negative 110 (new series). 



Navicida spima. Magnified 840 diameters, by Powell and 

 Lealand's immersion .^g. Negative 112 (new series). 



