BEALE'S CLASS MICROSCOPE. 105 



It should be added, that a novel and efficient form of 

 achromatic condenser is supplied with the instrument; 

 a series of small stops of various sizes are made to drop 

 into a minute hole drilled in the centre of the anterior 

 plano-convex lens, which convert it into a spot-glass, or 

 dark-ground illuminator. The whole is packed in a 

 mahogany case, and sold for 51. 5s. 



Fig. 59. Beetle's Clinical Microscope. 



Dr. Beale devised an exceedingly simple and con- 

 venient form of microscope, for the purposes of clinical 

 instruction and of class demonstration (fig. 59). Over the 

 body of the microscope, which is of small dimensions, a 

 tube is fitted with a Ttell-shaped mouth at the end. This 

 tube slides freely over the body, but is capable of being 

 fixed at will by means of a clamping-screw. The slide con- 

 taining the object is placed across the bell-mouth, and held 

 there by a spring pressing against the back of it, and is 

 thus maintained perpendicularly to the axis of the instru- 

 ment. "When the focus is adjusted the clamping-screw is 

 fixed, and the fine adjustment necessary for the differ- 

 ences of vision in different individuals is effected by 

 drawing out or pressing in the eye-piece. The object and 

 object-glass are thus protected from mutual injury, an 

 accident of by no means unfrequent occurrence in careless 

 or unpractised hands. In this form the instrument is 

 adapted to the clinical examination of secretions, &c. and 

 must be directed by the hand towards day or artificial 

 light. For demonstration to a class, this instrument is 

 attached horizontally to a small wooden stand by means 

 of a clamp, supported by two legs. To the stand a small 



