POWELL AXD LEALAND'S IMMERSION. 181 



would be the case if they were mounted on a flat 

 surface. It also interferes less than the old form with 

 the movements of the stage. 



Powell and Lealand's Immersion Condenser, or non- 

 achromatic condenser (fig. 112), is constructed on a 

 somewhat novel plan. It admits of a very large angle 

 of light, about 130 degrees, and allows of the use of 

 either central light, or one or two oblique pencils of 

 00 degrees apart. Two diaphragm slots (shown in the 

 woodcut apart from the condenser), fit in at A and B ; 



FIG. 113. Swift's Achromatic Condenser. 



by means of which two beams of light at right angles 

 can be used. The movement of these diaphragms is 

 effected by means of an outer sliding tube b with a slot 

 at the top, and into which the arm A fits; whilst another 

 at B gives a ready command of the rotation of the two, 

 either together or separately, thus producing consider- 

 able modifications of light. 



Swift and Son's Achromatic Condenser is conveni- 

 ently arranged to supply the place of a compound sub- 

 stage, and to receive accessory diaphragms. The optical 



