686 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



The result of tliis discussion shows that direct vision of solid 

 objects in the Microscope depends, with small amplifications, to a 

 preponderating extent on the capacity of accommodation of the eye. 

 The efficacy of this factor in small amplifications renders possible to 

 a considerable degree the appreciation of depth, which is the essential 

 postulate of eftective stereoscopic efifect in binocular vision. That 

 which is contributed by focal depth is under these circumstances 

 inconsiderable. With medium amplifications from 100 up to 200, 

 the efiect of accommodation no longer exceeds so greatly the focal 

 depth, and the total perspective of depth resulting from both factors 

 is reduced to a somewhat small fraction of the diameter of the field 

 of view. Its absolute amount still, however, reaches (even with such 

 amplifications) to hundredths of a millimetre with objects that are 

 in highly refracting media and with the use of small aperture-angles. 

 With high amplifications the efficacy of accommodation ceases almost 

 entirely, and the whole visual depth becomes more and more merely 

 focal depth. If the amplification reaches or exceeds 1000, the abso- 

 lute depth of the visual space is reduced to micromillimetres, and 

 finally to a fraction of /x. The microscopical images of solid objects 

 pass, in this case, more and more into pure transverse sections. 



The decrease of the visual space and corresponding thereto of the 

 depth of all objects capable of being conceived as plastic in binocular 

 vision, proceeds, with the smallest amplifications, approximately as the 

 square of the amplification, and therefore at first very rapidly because 

 with low powers the efiect of accommodation is what affects it almost 

 exclusively. With high amplifications, on the contrary, in which 

 focal depth only and no accommodation depth of any consequence 

 exists, the flattening of the visual space proceeds slower, and at last 

 progresses as the first power only of the amplification. 



The limited operation of stereoscopic apparatus for other than 

 quite moderate amplifications is therefore apparent. At the same 

 time we are able to gather some hints with respect to the conditions 



