132 



APPENDAGES TO THE MICROSCOPE. 



represented in Fig. 79, formed of plates and slips of plate-glass, 

 cemented together by marine glue ; of a loose vertical plate of 

 glass, just so much smaller than the front or back of the inside of 

 the trough as to be able to move freely between its sides ; and of 



a horizontal slip of 

 Fig. 79. glass, whose length 



equals that of the 

 inside-bottom of the 

 trough, but whose 

 breadth is inferior 

 by the thickness of 

 the plate just men- 

 tioned. The trough 

 being filled with 

 water (fresh or salt, 

 as the case may be), 

 the horizontal slip is 

 laid at the bottom, 

 and the vertical plate 

 is placed in contact 

 with the front of 

 the trough, its lower 

 left at the front edge 

 hold it there, acting as 



Zoophyte Trough. 



margin, being received into the space 

 of the horizontal slip which serves to 

 a kind of hinge ; a small ivory wedge is then inserted between 

 the front-glass of the trough and the upper part of the vertical 

 plate, which it serves to press backwards ; but this pressure is 

 kept in check by a little spring of bent whalebone, which is placed 

 between the vertical plate and the &ad;-glass of the trough. By 

 moving the ivory wedge up or down, the amount of space left 

 between the upper part of the vertical plate and the front-glass of 

 the trough can be precisely regulated ; and as their lower margins 

 are always in close apposition, it is evident that the one will incline 

 to the other with a constant diminution of the distance between 

 them from above downwards. Hence a Zoophyte, or any similar 

 body, dropped into this space, will descend until it rests against 

 the two surfaces of the glass, and will remain there in a situation 

 extremely convenient for observation ; and the regulating-wedge, 

 by increasing or diminishing the space, serves to determine the 

 level to which the object shall fall. — It is convenient for the 

 working Microscopist to be furnished with several simple Water- 

 troughs of different sizes ; and he may easily construct for himself 

 thin ones suitable for observing delicate Zoophytes or for growing 

 Chara or Nitella, in the following manner. A piece of plate-glass 

 of thickness equal to the water- space which it is desired to give, 

 is cut to the size suitable for the trough, and strips are cut from 

 three of its edges ; these strips are cemented with marine glue, in 

 their original relative positions, on a glass plate, so as to form the 



