16 On the High-Power Definition of 



V. — On the Sigh-Power Definition of Minute Organic Particles. 

 By Dr.KoYSTON-PiGOTT, M.A., F.E.S., F.C.P.S., F.E.A.S., M.E.I. 



Plate XXIII. 



Whenever ■we shall be able accurately to show a fine definition of 

 minute organic particles, great advance will have been made towards 

 the accurate discrimination of various diseased cells : and perhaps of 

 fluids hitherto undistinguishable under the microscope, though 

 organically different. 



But unfortunately such brilliant particles are halo'd with spu- 

 rious appearances in endless combinations. It is not my intention 

 here to enter upon the wide field of physiological research ; but I 

 imagine much that we have learned will have to be unlearned. I 

 here record my behef that the very best work that can now be done 

 towards perfecting our glasses is the development of the high- 

 power definition of organic particles. 



Nothing in the microscopic world is so difficult and nothing is 

 so much the subject of dispute, yet there are certain laws of the rays 

 of light which should be admitted and studied on all hands by those 

 who wish honestly to pursue this research. 



The first is the nature of the least circle of confusion and its 

 efiects. 



The second is the nature of vision when afiected by extreme 

 angular aperture. 



The third, the nature of a confusion of images when many 



EXPLANATION OF PLATE XXIII. 



By the courteous permission of Dr. Colonel Woodward, I have employed Mr. 

 Hollick to copy with the camera lucida the splendid photographs taken with the 

 one-sixteenth immersion lens at the Army Museum, Washington. The minute 

 tracery of the lithographs, visible with a lens, reflects great credit on the young 

 artist. 



Degceria domestica. 



Fig. 1 shows very beautifully the two black shadows sharply edging the 

 illusory markings, between which are sliown rudimentary beading, somewhat bar- 

 like. Just in the middle, two conterminous young tadpoles — as a lady calls the 

 curvicoUis " nails," — are plainly visible. 



Fig. 2 shows exactly the same part of tlie scale transformed into rouleaus of 

 continuous beading. With a pocket lens the admirable drawing by the camera 

 lucida can be better appreciated. Two distinct sets can then be seen, light and 

 dark. " The tadpoles " i» Fig. 1 are readily converted into long spotted forms by 

 a sufficiently good glass. The spherules of Fig. 2 take also a variety of shadows, 

 circular, crescentic or dotted, according to the direction, obliquity, and aperture 

 of the illuminating cone of rays. 



Podura curvicoUis. 



Fig. 3 shows a very fine definition of the " tadpoles," according to the light 



that is in them — an over-correction, which is generally found when a glass is 



adjusted to show their heads and tails, unspotted and unbeaded. But when the 



glass is of first-rate powers, these appearances give way first of all to markings 



