360 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



struction of the binocular microscope, since he states, in his 

 book, that in the binocular microscope there are not two dif- 

 ferent images, but the same image, presented to each of the 

 eyes of the observer. However true this may be of Powell 

 iSu Lealand's " binocular for high powers," it is not true 

 either for the Wenham, Nachct, or Stephenson binocular, or 

 for the Tolles binocular eye-piece. Indeed, with the Nachet 

 form, which has some advantages, the instantaneous conver- 

 sion of a relief into a depression, or vice versa, according to 

 the manner in which the images are made to enter the eyes, 

 is quite striking; and the very fact of orthoscopic or pseudo- 

 scopic vision thus produced, by alteration of the position of 

 the prisms, proves that the images are not similar. M. Ran- 

 vier states that he has found the penetrating power or focal 

 depth of the binocular superior to that of the monocular. 

 The reason for this is, that each eye uses only its own half 

 of the objective ; and any objective, when half the front is 

 covered, will, even with the ordinary monocular, have in- 

 creased focal depth. 



A moist chamber of very simple construction is described 

 by Dr. Strassburger. It consists of a ring of card-board 

 soaked in water, on which the covering-glass is placed. The 

 drop of water containing the Spiroc/yra, the copulation of 

 which was to be observed, must be suspended from the under 

 surface of the covering-glass, and may then be preserved for 

 several days; whereas, if placed under the covering-glass in 

 the usual way, the plants will invariably die. 



Self- centring Turn-table. 



A self-centring turn-table is described by Mr. C. F. Cox, 

 in which the slide is grasped at the two opposite corners by 

 right-angled clutches, which are moved simultaneously by 

 one milled head, turning a right- and left-handed screw. 

 As this device centres the slips only lengthwise, Mr. Cox 

 proposes, when it is necessary to make several cells in the 

 same slip, to hold the slide between two right-angled tri- 

 angles of brass, which are grasped by the clutches, the slide 

 being between them, and thus allowing several cells, if neces- 

 sary, to be made on one slide, by simply slipping it along 

 (American Journal of Microscopy, J an., 1878). 



