RECOLLECTIONS OF OUK MEETINGS. 19i 



detail as absolutely to require a hanl surface and the use of a 

 maguifyiug power to bring them out propei-ly. Many have ex- 

 perimented in this direction, but foremost amongst them all must 

 be reckoned Dr. Maddox, whose exquisite photographs of microscopic 

 objects have far surpassed anything that has been published in 

 Europe. Dr. Maddox favoured us with a visit at one of our recent 

 meetings, and exhibited there some of his latest productions, which 

 were most admirable, both in pictorial effect and faithful represent- 

 ation. Some of these pictures were of the mai'kings on diatoms, 

 such as Pleurosigma Formosum and P. Angulatum magnified 3,000 

 diameters, and were exhibited as tending to solve the question as to 

 whether they are in relief or not. For this purpose Dr. Maddox 

 views them stereoscopically, when most certainly this effect of relief 

 is produced. Some stereo -photographs of Pleurosigma Formosum 

 exhibited by him, when placed under the stereoscope, showed the 

 dots as hemispheres standing in closer proximity to the eye than the 

 surface of the frustule upon, which they appeared to be set ; in fact, 

 presenting the appearance uf so many minute ivory balls. Attention 

 was also drawn to the fact that some of the diatomaceous discs, when 

 viewed stereoscopically, are seen to be composed of two surfaces, au 

 outer and an inner one, with a certain amount of structure between 

 them. Mr. Bockett drew attention to an experiment of Mr. Beck's, 

 in which that gentleman photographed a portion of a glass tumbler, 

 on which the pattern was produced by hemispherical protuberances 

 " like so many plano-convex lenses on a convex surface," in which 

 photographs there was a tendency to exhibit these hemispheres as 

 hexagonals, according as their tops or bases were focussed by the 

 lens. 



We very much fear, however, that the stereoscopic test is hardly 

 reliable. Very considerable apparent moditioatious of form are pro- 

 duced by varying the condition of binocular vision. Apart from 

 the fact that if you change the pictures from one side to the other 

 you will find the relief become depression, and vice-versd, it will be 

 observed that if a perfectly flat picture be examined by a pair of short 

 focussed stereoscopic lenses it will appear to stand up precisely like 

 the field of a binocular microscope. Take a negative of a black disc 

 for instance, and print two copies of it either on glass or paper, place 

 the two side by side in a stereoscope, and although pictures of a 

 flat surface the effect will be that of a convex one. 



Apart from these considerations altogether, there can be no doubt 



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