260 



FRANCIS DARWIN. 



found that delicate trembling filaments darted out from the 



E-.EizzE^a 



Microscope electrodes. 



St, stage of microscope ; G, glass slip ; F, block of cork ; M, lump of 

 modelling wax ; w, w, fine wire passing through M ; B, end of w 

 connected with battery ; E, the other electrode fixed to F ; ob., the 

 object to be examined hanging in a drop of water; C, thin glass; T, 

 tube of microscope with objective ; S, a Strieker's binding screw ; G 

 is an ordinary glass slip, to which is cemented a cubical block of cork, 

 F, which supports the [fixed electrode. The latter is represented by 

 the black line, E. It consists of a sheet of platinum foil nearly as wide 

 as the glass slip to whose upper surface it is cemented, reaching from 

 E to the fixed block, F, it then passes up the vertical external face of 

 F, and bending at right angles ends in a point, and is cemented to the 

 upper surface of F and the undt-r surface of the thin glass-cover, C. 

 The movable electrode consists of a block of modelling wax, M, pierced 

 by a finely pointed wire, w (such as is used for clearing the canula of 

 a hypodermic syringe). To use the instrument, the object is placed at 

 ob, suspended in a drop of water, and w and E are connected with the 

 battery or Du Bois coil. For connecting the platinum plate E with 

 the coil a single one of Strieker's binding screws may be used. The 

 point w ought to stand up like a spring, so that by sliding up M, and 

 slipping 10 beneath the glass cover C, the point of w presses gently 

 against the under surface of C {w does not touch the under surface of C 

 in the figure). Supposing that a section of a teasel leaf is hanging at 

 ob, the point of w can be made to approach any desired filament ; when 

 this is effected the cube of modelling wax, M, is fixed by a little firm 

 pressure, to the glass slide, and on closing the key the filament is 

 subjected to the action of the current. 



