56 



THE MICROSCOPE 



Adjastable 

 trough. 



Lire box. 



Fig. 53.- 



-No. 3413, Slip with 

 Trough. 



convenient form mounted on a 3 X 1 slip ; it has usually a space 



for water about 2 mm. thick. It is made with an upper glass 



either of thin microscope cover 

 glass, about -25 mm. thick, or a 

 thicker glass about 1 mm. thick. 



Fig. 54 shows a glass trough 

 cemented together. This has 

 dimensions of 1^ XlJ Xj inches, 

 and is made of glass about 

 1 mm. thick. It is only suitable, 

 owing to the thickness of the 

 glass, for use with low powers. 

 A very useful form of trough, known as Beck's glass trough, 



is made of a 3 X 1 glass plate, into which arte fixed two screws 



and milled nuts, each holding a clamping plate. A half-circle 



of indiarubber made from an elastic band is laid on the 3x1 



shp, and a glass cover plate of any re- 

 quired thickness is placed on the top. 



The whole is clamped together by the 



milled nuts. As all the parts take to 



pieces, it can be readily cleaned, and 



cover glasses or separating bands of any 



thickness can be used. Separating bands 



of the very thinnest material, such as 



dental rubber, or even paper, can be 



used, so that the layer of material being 



examined is exceedingly thin. This is of 



great convenience when it is desirable to 



examine the specimens by dark-ground 



illumination or with high powers. It is a 



very convenient apphance also for the 



examination of aquatic specimens. These 



can be first arranged in position on the lower 3 X 1-inch slip 



within the area surrounded by the rubber band, the cover 



may then be placed in position and sufficient fluid dropped in. 



If a small circular cover glass be cemented in the centre of the 



3 X 1-inch lower glass, a small 

 drop of fluid can be confined to 

 the centre of the field for ex- 

 amination. It can be used with 

 substage condensers or dark- 

 ground illumiaators. 



A live box consists of a plate 

 3x1 inches, with an aperture 

 in the centre of which is fixed a 

 short brass tube carrying at the 



top a glass plate. Over this tube slides a cap, in the top of which 



a cover glass is held by a screwed cell. The object to be examined 



Fig. 



54.— No. 3415, 

 Trough. 



Fig. 



55.— No. 3416, Beck's 

 Glass Trough. 



