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V. — On Spurious Appearances in Microscopic Research. By 

 G. W. Koyston-Pigott, M.A., M.D. Cantab., F.C.P.S., 

 F.K.A.S., M.K.I., M.E.C.P., F.K.M.S., formerly Fellow of 

 St. Peter's College, Cambridge. 



Plate XI. (Upper portion). 



The " Battle of the Glasses " is gradually being fought out. But 

 until spurious appearances are no longer accepted as the true, it is 

 impossible that definition in the microscope can arrive at that 

 degree of perfection which is required by the spirit of the age. 



It has been my unpleasant task to point out the residuary 

 aberration of the best glasses, and until then unsuspected and stoutly 

 denied on all hands. This was followed by very considerable im- 

 provement. But the old school of microscopic belief still attracts 

 its disciples ; and I wish here to point out another glaring error in 

 definition, and an acceptance by such microscopists of the false for 

 the true. I had the honour of pointing out to the Fellows in 1869,* 

 the structure of the Lepisma Saccharina ; but as the remark has been 

 often reiterated by writers against my views that beads are merely 

 caused by the intersection of striae, and as the Lepisma has been 

 figured with such false beading, the accompanying Plate has been 

 drawn from the object in the field of view of the microscope by the 

 talented young artist, Mr. Hollich, to my complete satisfaction. 



The first figure on the Plate represents the spurious appearance 

 of exaggerated beads shown at the intersections of the upper and 

 lower ribs of the Lepisma at the part where they cross and inter- 

 sect at a considerable angle. In this case the objective was 

 improperly corrected for spherical aberration. In each of the 

 examples here described, the direct light of a good half-inch objective 

 used as a condenser is employed. The paraffin lamp flame is also 

 placed in the axis of the condenser. 



I now substituted an old one-eighth of 70° aperture, but a fresh 

 scale came into view in the positions of figures 2, 3, and 4. This 

 glass, made by Powell and Lealand about twenty-five years ago, has 

 the middle and back sets of lenses placed in contact ; we then saw 

 the form, Fig. 2, Plate XI. Each rib is terminated by an intensely 

 black point, and each rib towards the middle shows beautiful alter- 

 nate thinning and thickening of the ribs at regular intervals, the 

 intense black lines composing them showing rudimentary breakings 

 of their parallel rulings, but at the left side close imitations of the 

 Podura markings or spines accompanied by oblique shadows, the 

 spine bisecting the angle formed between the oblique shadows and 

 the ribs. On examining the beautiful drawing of Fig. 2 with a 

 pocket lens, these remarkable appearances will at once be evident. 

 * Page 303, vol. ii., 1869. 



