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' II. — On the Higli-Fower Definition of Organic Particles. 



No. II. 

 By a. W. KoYSTON-PiGOTT, M.A., M.D., F.R.S., &c. 



Plate XXVII. (Upper portion). 



The definition of a minute organic particle, as a subject of dis- 

 course, can never be exhausted till the microscope has reached the 

 last stage of improvement : probably in generations to come. 



To a great many microscopical people the denial of such defini- 

 tion is their stronghold, or citadel of defence. Errors and imper- 

 fections have for a long time prevented their definition. 



To declare, once for all, that the " tadpole markings " of the 

 Podura can only best be seen according to the notions of object- 

 glass makers when the glasses are spherically over-corrected, 

 doubtless will be received as rank heresy. This unfortunate error 

 in the making and testing of glasses pervades all Europe and 

 America. If a standard is all wrong, what becomes of the test ? 

 Galileo saw, instead of Saturn's ring, a planet with two smaller 

 ones touching it : that was all he could do with his antiquated 

 opera-glass. 



Mr. Stephenson has given us a splendid example of what can 

 be done by departing from the usual " humdrum " of work. 

 Boldly introducing the principle of developing new powers of 

 refraction in structure by choosing a refractive medium of the 

 highest refractive index ; we see how much the defining power of 

 the microscope has been exalted. Professor Walcott Gibbs con- 

 structed spectroscopes with a strong solution of phosphorus in 

 bisulphide of carbon, and obtained vastly superior powers of reso- 

 lution in the spectra. In the true philosophic spirit, we should 

 hail all attempts to detect error and elucidate truth with no nig- 

 gardly hand, and the thanks of our Fellows are warmly due to our 

 collaborateur Mr. Stephenson. Some three years ago I gave or 

 lent Dr. Maddox a slide in which I had rendered minute particles 

 much more distinctly visible by introducing a naphthaline solution 

 of india-rubber ; and the very low refractive index of the glass 

 spicules was described in the ' Quarterly Journal of Microscopical 

 Science,' supplied kindly to me by Dr. Bower bank. 



EXPLANATION OF PLATE XXVU. (Upper portion). 

 Beads of Crushed Podura JDegeeria. 

 Fig. 1. — Appearance of Crushed Podura Degeeria Beading, upper set. 

 „ 2. — Appearance of Crushed Podura Degeeria in another portion of the same 

 scale. 

 The colours of the beading varied with the slightest change of focus, three 

 different colours being distinguishable at one time in the same field. Exhibited 

 to Mr. Slack, Sec. R.M.S., F.G.S., at my house, latter end of July, 1873. 



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