1076 SUMMARY OF CURRENT RESEARCHES RELATING TO 



monocular, for it must be admitted that the monocular gives a decided 

 idea of solidity. For myself, I cannot see any difference in the stereo- 

 scopic effect between the binocular and monocular on that object 

 when it is placed in the position I have pointed out, although I have 

 repeatedly gone over the experiment with great care, and with a 

 perfectly unbiassed mind. 



Now turn the object round, so that the cut suctorial pipes lie in a 

 horizontal or east and west position ; the stereoscopic effect is so 

 marked that you might easily fancy you could crawl along the pipes. 

 When the object is in a vertical position, I would call the attention 

 of the observer to the loss of definition of all fine details which lie in 

 a vertical position. I allude to the minute hairs on the delicate 

 membrane which is stretched across the two cut suctorial pipes. 

 When the object is turned round, notice how sharp they become. 



To sum up, every exhibitor should be careful to place his object so 

 as to secure the largest amount of stereoscopic effect. It is, of course, 

 immaterial which way some objects are placed, such as a Goscinodiscus ; 

 but Isthmia, Pleurosigma, Navicnla, &c., should be placed with their 

 major axes east and west, as well as objects such as scales on butter- 

 flies' wings, and many others." 



Mr. Nelson further expressed " the hope that some one might be 

 " able to find out the cause of the difference, and to suggest a remedy." 



It may be that we underrate the difficulty which Mr. Nelson 

 feels on this matter, but we should have thought it almost unneces- 

 sary to point out that the maximum of stereoscopic effect is obtained, 

 ex necessitate rei, only when the object lies in a " horizontal " posi- 

 tion. In that position there is necessarily the maximum of displace- 

 ment of the images observed by the two eyes ; in the " vertical " posi- 

 tion this displacement is at its minimum, and the stereoscopic effect 

 is in great part lost.* 



Another and quite different point to be noted in explanation of 

 Mr. Nelson's difficulty is the reduction of aperture that takes place 

 in one direction with the Binocular, which we have already pointed 

 out in this Journal."!" This necessitates for the resolution of the 

 markings on diatoms, for instance, that the particular markings to he 

 resolved should be placed " east and west," but not necessarily the 

 major axis of the object, as directed by Mr. Nelson, a direction which 

 we fear will mislead some microscopists. 



Whilst pointing out that the explanation of Mr. Nelson's problem 

 is one that has been long recognized by microscopists, and presents no 

 such difficulty from a theoretical point of view as supposed, we quite 

 agree with him that it is but rarely that any practical effect is given 

 to the matter by exhibitors. 



Microscopes at the Inventions Exhibition. — The following Jury 

 awards have been made in respect of the Microscopes and Microscopic 

 Apparatus exhibited at the International Inventions Exhibition. 



To Messrs. R. & J. Beck a Gold Medal for " Microscopic and other 



* See further on this subject, this Journal, 1. (1881) p. 203, and iv. (1884) 

 p. 20. 



t See this Journal, iii. (1880) p. 874. 



