256 Transactions of the Royal Microseopieal Society. 



Note hy John Anthony, M.D. 



Having read Dr. Woodward's paper on the gnat and mosquito 

 scales, and looked carefully at tlie set of photographs in illustration, 

 which that gentleman has had the kind courtesy to forward to me, 

 I can come to no other conclusion but that what I have hitherto 

 regarded as real bead markings on the membrane in the intercostal 

 spaces on the scales from the body of the gnat are really and truly 

 spurious images, or, in the words of Dr. Woodward, " diffraction 

 appearances." 



Some two years ago, in the examination of a large number 

 of gnat scales, principally with the fine ith and xVth objectives of 

 Messrs. Powell and Lealand, such results were obtained that I 

 thought I had found in the scale from the body of the gnat an 

 excellent test for the " definition " of high-power objectives, inas- 

 much as there seemed, vnth. moderately oblique and well-corrected 

 light, what appeared to me triple rows of clearly defined beads 

 between the beaded longitudinal ribs of the scale ; and, as the same 

 appearances of beads were always manifest, and as those beads 

 always seemed to come out clearer when viewed with objectives 

 of well-known excellence, I trust to be pardoned for believing that 

 what I saw were not only real appearances, but that such objects as 

 the gnat scales might be of the greatest service to the microscopist 

 as tests for the defining qualities of high-power objectives. Under 

 such impression I made a careful drawing of the markings on the 

 gnat's scale under the most favourable conditions, and that drawing 

 I copied by means of photography; the photograph would have 

 been made directly from the scale of the gnat itself, but I had no 

 heliostat. These photographic copies of the drawing have gradually 

 passed into the hands of one or other of my microscopical friends 

 until the specimen forwarded with this paper is the only one left 

 to me. However, I have the negative, and if possible impressions 

 shall be printed for distribution among the members present at the 

 next meeting of the Society.* (PL CXXXIX.^ 



Taking the E, F, and G photographs of Dr. Woodward to be 

 the most characteristic, inasmuch as they show respectively two, 

 three, and four rows of beads as seeming to exist upon the same 

 scale under different conditions of illumination, I think one can 

 only look upon my drawing as a representation of very clearly seen 

 spurious beads. Of course it is not very flattering to one's amour 

 propre to have it shown so convincingly that one has taken the 

 shadow for the substance ; but I am assured that I shall have erred 

 in good company, inasmuch as the analysis of these diffraction 

 images will strike at the root of a vast number of descriptions of 



* Some were sent bj' Dr. Anthony to the meeting. 



