MO 



VI. — On the Markings on the Scales of the Amathusia Horsfieldii. 

 By Warren de la Rue, Esq., F.R.S. 



(Read December 20th, 1848.) 



Between two and three months since, my attention was directed 

 by Mr. Topping to some peculiar markings on the scales taken from 

 a wing of one of the Lepidoptera ; the peculiarity, in his opinion, 

 consisted in the markings being minute scales or featherings upon 

 the upper surface of the ordinary scale, certainly a very remarkable 

 structure if its existence were corroborated. With the view of test- 

 ing the accuracy of this opinion, the object was brought to me for 

 examination with a one-twelfth object-glass, as Mr. Topping had at 

 his command no power higher than a one-fourth of sixty degrees, 

 which he rightly judged was insufficient to enable him to form a cor- 

 rect opinion as to the reality of the structure exhibited. On sub- 

 mitting the scales to a scrutiny under a one-twelfth of one-hundred- 

 and-ten degrees aperture, the object being illuminated with a one- 

 fourth of sixty degrees, the illusion of the small featherings was 

 immediately dispelled, and the markings shown to consist of rows of 

 dots, immediately over the strise, or else to arise, partly or entirely, 

 from constrictions of the striae themselves. The real nature of these 

 markings, and their exact position on the scale have, however, been 

 the subject of much discussion amongst my friends ; and this is not 

 surprising, when we reflect that markings on one layer of a series of 

 superposed membranes, must necessarily interfere with the definition 

 of those on another, and that this difficulty increases as the thickness 

 of the membranes decreases. Hence the great desideratum of an 

 object-glass of large aperture, and allowing of sufficient distance be- 

 tween itself and the object, for illumination of the latter as an opaque 

 body by reflected light, such an objective would at once remove the 

 difficulty alluded to, as regards the outer surfaces of an object, and 

 would afford many other facilities in the investigation of minute 

 structures. 



With the idea that the distribution of lithographs of remarkable 

 objects amongst microscopists was desirable, I amused myself in my 

 leisure by making a drawing of one of the scales on stone, not intend- 

 ing to pursue the subject any further ; Mr. Topping, having, however, 



