60 The Microscope. 



which of course distorts its internal structure, and the sections will 

 not show the true structure. 



Rivet's pattern of microtome is the most convenient I have seen 

 for cutting such material. 



Wm, Humphrey, Adrian, Mich. 



2. Is there any definite rule for adjustment of cover-cor- 

 rection of objectives ? 



There is no one rule which can be easily made to work with all 

 objects. 



Correcting by coma is the one which is most generally to be relied 

 upon. With diatoms the apparent position of the marking serves as a 

 guide. Correction color is frequently made when the object is trans- 

 parent and well marked. 



A. Y. Moore, Cleveland, O. 



3. How can one best provide for preserving the life of a 

 species while studying its life history ? 



That depends certainly upon the object. Some objects keep well 

 in the animalcule slide of Prof. Weber. Others need a continuous sup- 

 ply of fresh water. For large objects Holman's Siphon-Slide is good. 

 There are many " Life " slides which are good, but a difficulty is gen- 

 erally found in keeping any object alive any length of time. 



A. Y; Moore, Cleveland, O. 



4. What objectives will constitute the best working series 

 for practical use with £-inch, 1-inch and 2 inch eye-pieces? 



My own experience would lead me to prefer a J-inch and £-inch. 

 The aperture in each case to be the greatest consistent with the best 

 chromatic and spherical corrections. 



If four objectives be allowed I should recommend a 1-inch, J-inch, 

 j-inch or J of 100° to 150° (air) and T V The last to be homogeneous 

 immersion and wide angle. 



A. Y. Moore, Cleveland, O. 



5. Where shall we commence to measure to obtain what 

 is called the standard length of a microscope tube ? 



I am unable to state with certainty, at present, but think from an 

 investigation of objectives that I am now making that it differs in 

 different objectives according to formula of construction, etc. 



A. Y. Moore, Cleveland, O. 



6. What is the best microtome for cutting vegetable sec- 

 tions, such as woods, barks, roots, etc.? 



