806 



SUMMA.EY OF CURRENT RESEARCHES RELATING TO 



Fig. 214. 



Lieberkiilm's Microscope. — The earliest representation we have met 

 with of this instrument is in P. van Musschenbroek's ' Essai de Physique,'* 

 tome ii. pi. xviii. fig. 6, and as we believe it to be hitherto practically 



unknown to English microscopists 

 we reproduce it in fig. 214. 



The following is a translation 

 of Musschenbroek's description (loc. 

 cit., p. 595) of the figure: — 



" There has also been recently 

 discovered a good way of strongly 

 illuminating large opaque objects, 

 so that they may be examined by 

 every kind of Microscope, even by 

 means of the smallest kinds. A A 

 is a small spherical concave mirror 

 of fine silver, well ground and polished, whence the light is reflected to a 

 focus on the object C, so that it is strongly illuminated at the back. This 

 mirror is pierced in the middle B, and the Microscope [lens or object- 

 glass] is there inserted and adjusted either forward or backward : the eye 

 is placed at D and the object is seen very clearly." 



Weinzierl's Simple Microscope for the Examination of Seeds-t— This 

 instrument (fig. 215), the invention of Dr. v. Weinzierl, consists of a solid 

 brass stand leaded at the foot, and carrying two arms jointed at c' and c, at 



the extremity of which are lenses 1 and 2. The arms move horizontally round 

 through the bearings at a and a', and they are fixed by the screws h and 

 h' in any desired jDosition. 



The weaker lens No. 1 is a simple biconvex lens 9 cm. in diameter, and 

 with a focal distance of 25 cm. It has a magnifying power of 2A times. 

 No. 2 is more powerful. It consists of two achromatic lenses 29 mm. in 



* 2 vols 4to, Leyden, 1739. f Zeitscbr. f. Wiss. Mikr., iv. (1887) pp. 42-4 (1 fig.). 



