Royal Microscojncal Society. 13 



Finally, in spite of the disadvantages and difficulties which seem 

 so far to attend this mode of examination of objects — difficulties 

 and disadvantages that in the light of more knowledge and more 

 exjoerience may be dissipated, I do occasionally get glimpses which 

 surprise me. I will not venture to pronounce an opinion upon 

 them, but merely lay the whole matter before you as a subject 

 worthy of careful exploration, and certain to yield most interesting 

 results. I notice that, whatever other adjustments are necessary as 

 regards the correcting collar of the observing objective or the apla- 

 natic searcher itself, it seems to be imperative that a distance of not 

 less than seven inches shall be kept between the eye-piece and the 

 searcher, at risk of cutting the margin of the field of view. 



It was my intention to have exliibited an experiment with it, 

 but the accident to my 1-inch objective has warned me not to 

 attempt it under circumstances so unfavourable to perfect success 

 as the present occasion, but I hope to do so ere long. I append an 

 extract from one of Dr. Maddox's letters to me on the structure of 

 scales, and I look forward to further observations by him in eluci- 

 dation of many difficult portions of the subject, especially the chi'o- 

 matic effects : — • 



Extract of Letter from Br. Maddqx. 



" My object was to try amongst the readily procurable and 

 ordinary scales the effect of various chemical and destructive agents, 

 and I fancy by these means we may make out much of their struc- 

 ture aided by the microscope, though with it alone I fear we shall 

 be constantly verging on the dubious. Whatever the surfaces, there 

 appears a framework amongst them which is connected to the inner 

 surfaces, and the nearer the form of it corresponds to small squares, 

 the nearer the approach to beading, and the coarser at the corners 

 or junctions the more resemblance to spherical embossings. 



" These spaces seem to be filled with a greasy matter partly 

 soluble by boiling in liq. amm. fort., then treating with chloro- 

 form at a boiling point — performing these operations on the slides, 

 and allowing the soluble matter to be washed away by the solvent 

 last used. Then staining the scale with aniline or other suitable 

 material and mounting in a dry state, also in a dense liquid satu- 

 rated solution of acetate potassae, &c. — or boiling in liq. potassae, 

 washing with distilled water, then with ether and chloroform — and 

 drying by heat — in fact varying these agents ; also using turpentine 

 to boil these scales in, and then permitting some thin coloured resin 

 in solution in turpentine to flow over them and dry by heat. Nu- 

 merous methods were tried and under high powers, advantageously 

 as regards structure." 



