The Microscope. 83 



anything of the kind ; at least he stands alone in making the 

 assertion. 



MARINE GLUE. 



This is a solid that can be used only with the application of 

 heat. It is troublesome, but one of the most tenacious of 

 cements for fastening metal rings to glass and for similar pur- 

 poses, yet the beginner can easily get along without it. To use 

 it, the cement, the slip and the ring must be heated, and the 

 fingers are frequently uncomfortably heated as well. It is com- 

 posed of India rubber, shellac and naphtha melted together and 

 allowed to cool. 



The dealers suppl}^ a liquid marine glue that may be used 

 without heat. It is said to have almost as great adhesive power 

 as the ordinary solid form. I have had no experience with it 

 and have nothing to report from the experience of others. 



RINGS FOR DEEP CELLS. 



It often happens that it is necessary to mount a large or a 

 thick object, and that a cell deeper than the ordinary kind is 

 needed. To build up these deep cells with cement is neither safe 

 nor convenient. If made of several layers applied on one an. 

 other the cell is more likely than not to leak, because the walls 

 easily crack or separate slightl}^ from the glass and allow the 

 air to enter and the mounting medium to ooze out. And to 

 make these deep rings is not eas}^, as the first layer of cement 

 must be allowed at least partly to dry before another can be 

 added, and this takes time, sometimes a good deal of it. A 

 better way is to fasten a deep metal or other ring to the slip, 

 and thus to make a cell of almost any depth, the latter of course 

 depending upon the thickness of the circle used. The rings are 

 for sale by the dealers and are of brass, tin, glass, rubber or of 

 some other serviceable material. With the exception of the 

 glass rings and the cheapest brass ones, they must all be 

 bought ; but these exceptions are usually all that the micro- 

 scopist will need and are as useful as those that are purchased. 

 The home-made glass rings are admirable, although their edges 

 maj^ not be as smooth as the edges of those bought at an enor- 

 mous price from the dealers ; but the satisfaction of making 

 them and of thus being independent of all outside help, atone 

 for rough edges and for somewhat irregular appearance, espe- 



