( 184 ) 

 COEKESPONDENCE. 



Mr. Cundel's anxiety for the Credit of thi8 Journal and 

 Sir David Brewster's Soientifio Eeputation. 



To the Editor of the ' Monthly Microscopical Journal.' 



Mb. Editor, 



Sir, — Whilst admitting the intended courtesy of Mr, Cundel's 

 letter upon some remarks which I had the honour of addressing 

 on the 3rd January last to the President of the Eoyal Microscopical 

 Society, in which he appears to call me to account " for the credit 

 of the ' Microscopical Journal,' and in justice to the scientific 

 character of the late Sir David Brewster;" I may be allowed to reply, 

 fii'st of all, that it may be safely assumed that the credit of this 

 Journal is quite secure under the protection of its present Editor ; 

 and, secondly, that no puny efforts of mine could possibly injure the 

 world-wide reputation of Sir David, of whose writings I am an admir- 

 ing student. 



Now, Sir, though IVir. Cundel complains thus of my statements 

 (rather curtly reported), I hope he is not a j)hotographer, lest Sir 

 David's own words should further on meet his unqualified disapproval. 

 If Mr. Cundel would have given himself time and opportunity for 

 reading Sir David's ' Optics,' he would have saved me the trouble of 

 encroaching on your valuable sjiace. 



Sir David excited the wrath of photographers in general by his 

 unsparing criticisms bestowed upon wide-angled lenses, and I shall 

 make a few extracts from his writings to illustrate this point, in 

 deference to Mr. Cundel's wish. Amongst other things Sir David 

 says : — 



" As the pupil of the human eye is little more than two-tenths of 

 an inch in diameter, we may regard the picture on the retina as a 

 correct representation of external objects, in so far at least as its correct- 

 ness depends upon the size of the lens which forms the picture . . ." 



'• Let us suppose that a lens four inches square is employed to pro- 

 duce upon a plane surface the image of any object, and that the size of 

 the pupil of the eye is two-tenths of an inch ; then, as there will be 

 several hundred areas equal to that of the pupil in the leus, the image 

 given by the lens will be a compound imago consisting of 6evei*al 

 hundred perspective views of the object taken from several hundred 

 diftcrent points of sight, each distant two-tenths of an inch from its 

 neighboui', and all those on the margin of the lens distant three inches 

 and eight-tenths from those ojiposite to them. Such a jumble of 

 images cannot under any circumstances be a true representation of the 

 object." 



" Let us now apply these results to the photographieal pictures of 

 the himian bust as taken in a camera. The human face and head 

 consist superficially of various surfaces, some vertical, some horizontal, 

 and many inclined at all angles to the axis of tlie lens by which they 

 are represented on a plane surface 



