232 SUMMARY OF CURRENT RESEARCHES RELATING TO 



" To which are we to give more weight, bearing in mind that the 

 essence of stereoscopic effect lies in viewing a great number of planes 

 simultaneously ? Should we adapt our instrument for the single plane 

 in true focus, or for all those others seen at the same time ? I think you 

 will find it rational — the more so as, even in the single plane, we can- 

 not secure equally good resolution in all directions — that we should 

 extend a good deal of consideration to all those other layers ; and the 

 best rule to be followed — one which I believe Mr. Taverner, from his 

 experiments in stereoscopic photomicrogaphy, has also anived at — 

 is : use circular stops (as in fig. 41), .having them just small enough to 

 secure a moderately fair image of the deepest layers which it is re- 

 quired to see simultaneously with the others. In other words, get the 

 necessary depth of focus, but no more ; for in securing more, the per- 

 fection of the image in other parts is being decreased. Similar objects 

 being exhibited under binocular j\Iicroscopes in which this rule has 

 been followed, and under others in which the two halves of the objec- 



FiG. 41. 



tive are left as usual, the improved effect in the former is perceptil)le at 

 a glance." 



The best position for the stops is discussed, and it is suggested that 

 immediately below the Wenham or Riddell prism is the most suitable 

 place, and that a sliding carrier for the stops in this position would be 

 the most convenient plan. 



After touching on the difficulties connected with stereoscopic effect, 

 when high powers are used, the paper concludes with remarks on the 

 points of difference between stereoscopic vision with binocular Micro- 

 scopes and stereoscopic photomicrography. 



(6) Miscellaneous. 



Mendelism and Microscopy.*—!). J. Scourfield, in the course of a 

 paper on the above subject, suggests that systematic researches on 

 microscopic creatures might do much to correct and extend our know- 

 ledge of Mendelism. It is necessary that such creatures should be 

 bisexual, and not too small to prevent the isolation and control of 

 individuals. Their small size would make it possible to carry on 



* Journ. Quekett Micr. Club, ix. (190G) pp. 395-422 ; also in extract form. 



