ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 501 



Hodgkinson, A.— On the Diffraction of Microscopic Objects in Relation to the 

 Resolving Power of Objectives. 



Pror. Manch. Lit. and Phil. Soc, XXV. (18S6) pp. 263-7 (5 figs.) and 



pp. 223 and 271-2. 

 James, F. L. — Nobert's Bands. 



St. Louis Med. and Surg. Journ., LIV. (1888) pp. 166-7. 



L., A. S. — Powers of Eye-pieces. 



[" Table of the powers of the eye-pieces of different makers as deduced from the 

 total magnification with the 1 in. objective.''] 



Engl. Mech., XLVII. (1888) p. 146. 



Queen, J. W.— Apparent and Actual Size of Field, Magnifying Power, &c. 



Queen's Micr. Bulletin, V. (1888) pp. 1-2. 

 „ General Hints on the use and care of the Microscope. 



Tlie Microscope, VIII. (1888) pp. 4-5. 

 Royston-Pigott, G. W. — Microscopical Advances. XXXV., XXXVI. 



[Eesearches in High Power Definition. Interference lines, circles, and dots. 

 Attenuated lines, circles and dots.] 



Engl. Mech., XLVII. (1888) pp. 137 (2 figs.), 226-7 (2 figs.). 



W I e neb, 0.— [Measuring Thin Films.] 



[" In an exhaustive paper upon methods of measuring thin films, Otto Wiener 

 makes certain measurements of the thickness of a film of silver which can 

 just be perceived by the eye, and arrives at the conclusion that 0*2 millionths 

 of a millimetre is an upper limit of the diameter of a silver molecule."] 



The Microscope, VIII. (1888) p. 93, from Scientific American. 



Zegh, P.— Elementare Behandlung von Linsensystemen. (Elementary treatment 



of lens-systems.) 8vo, Tubingen, 1887, 



(6) Miscellaneous. 



Heather's ' Mathematical Instruments.'— It is really a disgrace to 

 all concerned — publishers and editor — that this book with a title-page 

 of 1888,* should have been published. 



It is inconceivable that any intelligent grown-up person should not 

 have known that the extracts we print below are an anachronism in this 

 year 1888 or even in the year 1848. Imagine, for instance, describing 

 any Microscope of this date as having the " amplifying lens" of the old 

 makers. 



" The compound or achromatic Microscope consists of four lenses 

 and a diaphragm, placed in the following order : the object-lens, the 

 diaphragm, the amplifying lens, so-called because it amplifies or enlarges 

 the field of view, the field-lens, and the eye-lens. The relations 

 between the focal lengths and intervals of the lenses, and the distance 

 of the diaphragm from the object-lenses are determined so that the 

 combination may be achromatic, aplanatic, and free from spherical con- 

 fusion. The field-lens and eye-lens form what is called the eye-piece, 

 and the object-lens and amplifying-lens form, or tend to form, an 

 enlarged image of the object in the focus of the eye-piece, which image 

 is viewed through the eye-piece " (p. 79). 



The following paragraph is also deserving of note : — 



" The best Microscopes are constructed with compound object-lenses, 

 which are both achromatic and aplanatic, and by this means the 

 aperture, and consequently the quantity of light, is much increased. 

 Good compound lenses possessing the required properties have been 

 formed of a concave lens of flint glass placed between two convex 

 lenses, one of crown glass and the other of Dutch plate " (p. 79). 



* Heather, J. F., ' A Treatise on Mathematical Instruments, their construction, 

 adjustment, testing, and use concisely explained.' 14th ed., revised, with additions 

 by A. T. Walmialey. 8vo, London, 1888. 



