12 Transactions of the 



could fit up my second microscope with equal power, exactly simi- 

 lar illumination and duplicate objects, and place both microscopes 

 so that I could look first into one, and then into the other, without 

 getting ofi" my chair, I determined to put the plan in practice ; and 

 accordingly did so. As before, comparisons were odious. The 

 image was much clearer and better defined in the microscope where 

 the amplification was obtained in the objective only, than in the 

 other. I think on this latter occasion the definition was at least as 

 good as the best I ever saw under Dr. Pigott's own microscope ; 

 and certainly it was greatly superior to that given in his instrument 

 at the meeting of the Koyal Microscopical Society in October last. 

 (I mention this to show my conviction that there is no material 

 difference between the searcher he uses, and the one * lent to me.) 



The objects which he has hitherto exhibited are not by any 

 means crucial tests. They are P. Formosum (dry), scale of JDegeeria 

 domestica, and scale of Macrotoma (named on Dr. Pigott's slide 

 Podura ]jlumhea'\) . I have always been under the impression that 

 I had seen them better without any searcher at all, in the micro- 

 scopes of Dr. Gray, Mr. Fitz Gerald, and Mr. Delferrier, and also 

 in my own ; and there is evidence in the celebrated American pho- 

 tographs of the Test-Podura scale (Lepidocyrtus ) that the so-called 

 beads have not been wholly obscured from view. 



I know that the lens I have used is not the exact combination 

 which Dr. Pigott has had made, but I get precisely the same abun- 

 dance of beads as he describes ; and the same abundant display of 

 brilliant blue and yellow, green and ruby effects which he dilates 

 upon are associated with all its best performances. Moreover, there 

 is the same subtilty of adjustment of which he speaks — a difficulty 

 which Dr. Maddox (I believe) finds nearly unsurmountable : a point 

 upon which I also can speak feelingly, since I damaged my " fifth " 

 objective (by Smith and Beck) in the endeavour to obtain it accu- 

 rately. Then there is the occasional excellent definition to counter- 

 balance the unbelief which so lavish a display of colour in objects, 

 usually transparent, infuses into one's mind.^ 



* I retain the term '' aplanatic searcher ' in speaking of this contrivance, for 

 the obvious reason that Dr. Pigott has used it, and until Dr. Pigott corrects me I 

 must still believe that it is properly so called. 



t The genus Podura is non-scule-bearing, and is represented by the active black 

 insect which skips over the surface of the Hampstead Ponds, looking at a distance 

 like a quantity of soot on the surface of the water. 



+ Dr. Maddox writes to me that he did not get on well with the aplanatic 

 searcher which Dr. Pigott was good enough to lend him. He says its value 

 seemed to be chiefly in tlie facility with which many structures gave complemen- 

 tary tints very defined, thus facilitating the study of tissues of diflerent thickness. 

 But he further says the results were better than those obtained by amplification 

 with an ordinary objective of low power at the end of the draw-tube, — a plan he 

 has tried in company with the late E. Beck ; and does not seem to value results 

 of this kind, unless daylight and artificial illumination tell the same tale. He 

 also makes some valuable observations upon chromatic phenomena, which I have 

 asked him to put in a convenient form, as they are likely, as mere extracts, to 

 lose much of their force. 



