28 THE MICROSCOPE. Feb., 



rule. This will give the magnification of the combination. 

 Then the combined power divided by the known power of the 

 objective will give the power of the eye-piece. Prof. J. Edwards 

 Smith, in his work, " How to see with the Microscope," gives 

 the true magnifying power of single convex lens at ten inches, 

 as lollows : 



One inch equals 8 diameters; i inch equals 38 diameters; i 

 inch equals 58 diameters ; 1-10 inch equals 98 diameters. An 

 objective properly rated, of 1 inch focus, should magnify 8 di- 

 ameters, and with a one-inch eye-piece at ten mches, should 

 magnify 64 diameters. 



219. How may the owner of a small aquarium like that of Tempere^ 

 learn to identify theformsf — Dalton. 



Stokes' Microscopy for Beginners — price $1.50 — will give the 

 needed information. It tells all about life in our ponds and 

 ditches. 



220. Where can I obtain the latest edition of Griffith and 

 Henfrey's Micrographic Dictionary? — I. H. H. 



The Micrographic Dictionary is published by John Van 

 Voorst, Paternoster Row, London. It is listed by Bausch and 

 Lomb Opt. Co., Rochester, N. Y., at S20.00 net. 



PRACTICAL SUGGESTIONS. 



By L. A. WILLSON, 



CLEVELAND, OHIO. 



Magnification. — Mere amplification of an object is useless 

 for nearly all purposes. Definition and disclosure of detail are 

 of scientific value. Never use upon an object a higher power 

 than is necessary to show it well. 



Killing and Preserving Delicate Organisms. — Perchloride 

 of iron is one of the best agents for this purpose. The organisms 

 referred to are such as Rotifer vulgaris and other ciliata. With 

 this agent the animals are fixed very perfectly in their expanded 

 condition nicely exhibiting their cilia. For ordinary use a so- 

 lution in alcohol containing about two per cent of the compound 

 should be used. 



The animals may be placed on a slide without cover and the 



