72G SUMMARY OF CURRENT RESEARCHES RELATING TO 



If the optical constants should be : </> = 45°, / = 204 mm., and 

 w — 0*2 mm., then for every uncertainty of ± 0*1 of the scale reading, 

 a corresponding uncertainty of ± 4 • 9, or ± 2 • 5 units of the fifth decimal 

 place is produced in the value of A n. 



(6) Miscellaneous. 



Thompson's Optical Tables and Data. — These are intended by their 

 compiler, Dr. Si Ivan us P. Thompson, for the use of opticians, and his 

 name, is an ample guarantee for the efficiency of the collection. Tbe 

 tables number 93 in all, and the following list will give an idea of their 

 character. Nos. 1-13, Logarithmic relations of British and metric 

 measures. 14, 15, Velocity of light, and wave-lengths. 16-26, Refrac- 

 tive indices of various glasses, liquids, and minerals. 27-56, Sphero- 

 meter, optical formulas, lenses, prisms, combinations. 57-64, Chromatic 

 and spherical aberration. 65-68, Magnification. 69-71, Eye and pres- 

 byopia. 72, 73, Eefractive indices of fluids used in Microscopy, tube- 

 length of Microscopes. 74, Magnifying power of Microscopes, standard 

 screw. 75, 76, Numerical aperture. 77-80, Eesolving power of objec- 

 tives, depth of vision, and penetrating power. 81, Diffraction. 82, 

 Distance of optical lantern from screen. 83, 84, Reduction and enlarge- 

 ment. 85—93, Eye-sensation to different lights, photometry, colours of 

 thin films. The tables are preceded, wherever necessary, by full ex- 

 planatory sections, and are accompanied by diagrams. The print is 

 clear, and the book is likely to be an indispensable auxiliary to all inter- 

 ested in practical optics. The publishers are Messrs. E. & F. N. Spon. 



Resolution of Striae.* — Dr. E. H. Ward, of Troy, N.Y., recom- 

 mends, for the resolution of striae, &c, the old method of obtaining 

 oblique light by the decentralisation of the substage condenser. 



The late Mr. Herbert R. Spencer. — We regret to have to record 

 the death, on February 7th, in the 51st year of his age, of Mr. Herbert 

 R. Spencer, Superintendent of the Spencer Lens Company. Mr. Spencer 

 was born in the little rural village of Canastota, N.Y., where his 

 father, Mr. Charles A. Spencer, had established, in a rude workshop, a 

 manufactory of Microscope objectives of such excellence that they soon 

 attracted the attention of the scientific world, and obtained the highest 

 award from the Paris Exhibition. In 1873, the Spencer workshop at 

 Canastota was destroyed by fire, including nearly all the tools and 

 machinery. In 1875, the firm moved to Geneva, N.Y., where, for 

 about two years, they were connected with the Geneva optical works. 

 Mr. Spencer's father died in 1879. After several changes, in 1890, 

 Mr. Herbert R. Spencer settled in Buffalo, N.Y., in partnership with 

 Mr. Frederick R. Smith ; and, in 1895, became Superintendent of the 

 "Spencer Lens Company" of Buffalo. The foregoing particulars have 

 been furnished to us by Dr. John A. Miller, of Niagara University, Buf- 

 falo, from a biographical sketch of the late Mr. Spencer, by Dr. George 

 E. Blackman. 







Scales, F. Shillington — Microscopy for Beginners. 



[A series of articles.] Science-Gossip, July 1900 et seq. 



* Trans. Amer. Micr. Soc, 1900, p. 111. 



