DE. LIEBERKUHN'S MICROSCOPE 



139 



as in Hooke's ; the ball L could be tightly clamped by the screw 

 collar M, in which slots were cut to give spring. (4) A condensing 

 lens on jointed arms appears ; this probably was the first application 

 of such adjustments to the con- 

 denser. From the singular posi- 

 tion of the candle beneath the 

 condenser, we may infer, without 



doubt, that the mirror was still II A%, ^b A I A 



unknown as a microscopical ac- , 

 cessory in England. 



In fact, in no microscope up 

 to this time has there been any FIG. 107. Lieberkiihn's microscope (1739). 

 trace of, or reference to, a mirror ; 



but in 1716 Hertel employed it and introduced some other consider- 

 able modifications. The * general appearance of the instrument as 

 originally figured by Hertel is given in fig. 105. Not only have we 

 the mirror below the stage, but also above 

 the stage a concave metal mirror reflecting 

 light through a condenser on the object, 

 while the stage has focussing movement by 

 the right-hand ornamental 'butterfly' nut, 

 and is capable of movement to and from the 

 pillar by the middle nut, and also of rotary 

 movement by the left-hand nut. These two 

 last movements form what is now known as 

 a 'mechanical stage.' The body-tube is 

 hinged and is inclined by a screw-sector 

 mechanism. A distinct advance on the simple 

 microscopes which had preceded it was made 

 by one devised by M. Joblot, and illustrated 

 in fig. 106. The ornamental plate holds the 

 lens, the focus being adjusted by the nut and 

 screw ; the plate next to the ornamental one 

 is a concentric rotary stage, of good mechanical 

 quality. The tube A was called by Joblot 

 ' the Canon,' and was lined with black cloth 

 or velvet, and has a diaphragm at each end. 

 These diaphragms are movable, which was 

 practically a considerable optical benefit. 



In 1738 Dr. N. Lieberkiihn devised, 

 what had been employed in principle by 

 Descartes a century before, 1 the instrument 

 that has ever since been known by his name, 

 and which is still of considerable value to the 

 microscopist. Fig. 107 is a reproduction 



from the earliest drawing known of Lieber- p IG IQS Culpeper and 



kiilm's microscope. A A is a concave mirror Scarlet's microscope (1738). 

 of silver ; from its form the light is reflected 



from it to a focus on the object C. The mirror is pierced in the 

 centre at B, and the lens, or object-glass, is inserted and adjusted, 



' See pp. 126-7. 



