ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



863 



Fig. 188. 



Fig. 189. 



from the squares traverses the lens, is reflected on the plane and 

 directed upwards again and focused in the plane of the diaphragm. 

 The carrier is moved until the image is seen 

 sharp in the eje-piece, and the focal plane 

 of the lens L coincides with the plane of 

 the diaphragm; the reading of the vernier 

 is taken, allowance being made for the shape 

 of the lens, its thickness, &c. 



The image, consisting of luminous lines 

 on a black ground, is easily seen ; the light 

 traverses the lens twice, and doubles its 

 defects. The focus is very precise, so that 

 by covering up portions with small screens, 

 the variations in the curves can be estimated 

 by the differences in their acuteness, and the 

 sharpness will indicate the quality of the 

 lens tested. 



White or monochromatic light is used 

 for illumination. Eeflected light enables 

 each surface to be tested separately, while 

 the estimation of the combination of surfaces 

 and media is effected by means of the re- 

 fracted image. 



Instructions are also given for using the 

 apparatus for concave mirrors, diverging 

 leuses, convex surfaces, spheres and cylin- 

 drical surfaces. 



The author claims that the apparatus is an accurate focimeter, of 

 general application to all curved surfaces ; the precision may be 

 carried to a high degree where necessary, and in ordinary cases it 

 provides ready means of seeing at a glance and without preparation 

 the quality of an optical system. 



Gundlach's Improved Objectives.* — The Gundlach Optical 

 Company are now making objectives " after the new principle dis- 

 covered by Mr. Gundlach. "f 



" The water-immersion objectives have a very long working dis- 

 tance and the aberrations of higher order are corrected to a much higher 

 degree than was heretofore possible in a water-immersion objective ; 

 hence, these objectives have a definition and resolving power found in 

 oil-iramersion objectives only. This series of objectives may there- 

 fore be regarded as a new improvement in the field of microscopic 

 apparatus, a water-immersion objective of highest optical quality 

 having also a long working distance." 



Series of Objectives. — Mr. J. C. Stodder sends us the following 

 note of tlie hitc ii. iJ. Tollcs's views of the best scries of four or five 

 oV>jectivoH, to cover as far as possible the whole range of " general 

 micro8copy." 



"For four only— 3 in., 1 in. (30^), 4/10 in. (110^ dry), 1/10 in. 



* Amor. Mon. Micr. Journ., vi. (18x5) pp. loO-l. 

 t Bee this Journal, ante, p. 705. 



