Microscopical Essays, 



KL is the Aider-holder, which fits into a hole that is in /he 

 middle of the ftage N I S ; it is ufed to confine and guide either 

 the motion of the Aiders which contain the objects, or the glafs 

 tubes that are defigned to confine fmall fi flies, for viewing the cir- 

 culation of the blood. The Aiders are to be pafled between the 

 two upper plates, the tubes through the bent plates. 



L is a brafs tube, to the upper part of which is fixed the con- 

 denfing lens before fpoken of ; it fits into the under part of the 

 Aider-holder and may be fet at different diftances from the 



object, according to it's diftance from the mirror or the candle, 

 This tube is feen further drawn out in Fig. 2, Plate IV. 



O is the frame which holds the two refiecling mirrors, one of 

 whieh is plane, the other concave. Thefe mirrors may be moved 

 in various directions, in order to refiecl the light properly, by 

 means of the pivots on which they move, in the femicircle Q 

 S R, and the motion of the femicircle itfelf on the pin S ; the 

 concave mirror generally anfwers beft in the day-time ; the plane 

 mirror combines better with the condenfing lens, and a lamp or 

 candle. At D there is a focket for receiving the pin of the arm 

 Q, Plate IX. to which the concave fpeculum, for refiecling light 

 on opake objecls, is fixed.. 



At S is a hole and Ait for receiving either the nippers L } Plate 

 IX. or the fiffi-pan I ; when thefe are ufed, the Aider-holder mufi 

 be removed. 



% a hole to receive the pin of the convex lens M, Plate IX. 



