132 



THE MICROSCOPE AND ITS REVELATIONS. 



Bockett (Fig. 108). It is preferable, however, to surround the glass 

 chimney by a cylinder of porcelain, having a large aperture on one side 

 for the passage of the light; and this may be advantageously blackened 

 on the outside, contracted above into a cone, and furnished with a shade 

 over the aperture (as in Mr. Swift's construction, Fig. 109), so that as 

 little light as possible may enter the eye of the observer, except that 

 which proceeds from the object. The lamp should be so hung as to be 

 capable of being rotated on its own vertical axis; so that either the whole 

 breadth of the flame, or its edge only, may be turned towards the mir- 

 ror or condenser, according as diffused or concentrated light is required. 

 In Mr. Swift's Lamp (Fig. 110), the Bull's-eye is mounted on a separate 



FIG. ioy. 



PIG. Ho. 



Chimney and Shade of Swift's 

 Microscope-Lamp. 



Swift's Microscope Lamp. 



stem, capable both of vertical elevation and of horizontal adjustment, 

 which rises from one end of an arm that is pivoted beneath the base of 

 the brass cylinder that carries the lamp; and from the other end of this 

 arm there rises a second stem, carrying a speculum, from which addi- 

 tional light may be reflected when desired. By rotating this arm on its 

 pivot, the speculum and condenser are shifted together, so as to direct 

 the full power of the flame wherever it may be required; an arrangement 

 especially convenient for the illumination of opaque objects. As it is 

 often found extremely difficult to obtain an exact centering of the illumi- 



