246 MEMORANDA. 



miniature as that by which the plates of Auers' " nature- 

 printing " are formed. Take some perfectly clean and bright 

 tinfoil, three or four times doubled, and lay it upon a smooth 

 block of metal. On the upper surface of the foil place the 

 object ; hold upon this a short steel punch with a highly- 

 polished face, and strike it a smart blow with a hammer. In 

 this way fish-scales, feathers, and sections, may be fairly 

 impressed in the tin. For delineation of surface this process 

 is not much to be depended upon ; for if contiguous parts of 

 the object are hard and soft, or more or less elastic, it will 

 develop markings where they do not really exist. As an 

 example, when a mouse hair was copied by the electrotype, 

 it was shown to be nearly smooth, but when stamped into the 

 foil, all its characteristic pigment-cells were displayed in the 

 metal in a very beautiful manner. It has often been thought 

 that these cells are real external cavities ; which appearance is, 

 doubtless, a deception of refraction. The last operation also 

 displays some singular peculiarities in other animal hairs. I 

 think that it would be an improvement to make use of a 

 fly-press instead of the hammer and punch. — F. H. Wenham. 



IVote on Dr. Griffiths' Paper on Angular Aperture. — We have 



received a communication from Dr. D'Alquen, containing 

 " Further Remarks on Dr. J. W. Griffiths' Paper, on the 

 Angular Aperture of Object-glasses, &c.," in which that 

 gentleman complains in very strong terms of the way in 

 which his objections are noticed by Dr. Griffiths in the 

 Micrographic Dictionary, Art. Diatomaceae, p. 203. And in 

 support of his own views, he states that they had elicited 

 the spontaneous approval of one of the best authorities on the 

 subject, who had written to him to the following effect: — 



" I have, however, to congratulate you upon the plain and 

 matter-of-fact method by which you refuted Dr. Griffiths' 

 visionary theory, and which I think he will find it difficult to 

 answer, even if he should feel so inclined." — Editors. 



ERRATA. 



Page 110, Hue 35, for solid, read sold. 

 „ 119, „ 36,/orPlateIX.rmfZ Plate VII. 

 ,, 124, ,, 22, /or soniferous, reacZ coniferous. 



