CHAPTER XIII. 



PHILOSOPHICAL, OPTICAL, AND MATHEMATICAL 



INSTRUMENTS. 



Thermometer frames and scales. Telescopes. Gas bags. Gasometers. Hydrostatic bellows. 

 Opera glass cases. Quadrants. Barometers and chronometers. Water levels. Squares and 

 bevels, curves, triangles, and parallel rules. Reel measures. Leveling rods. Dry measures. 

 Wine measures. Scales and rules. Instrument cases. Instrument handles. 



There are a variety of instruments and appliances under this 

 head, for which the caoutchouc fabrics and compounds are found 

 useful ; among them the following may be noticed. 



THERMOMETER FRAMES AND SCALES, 



Thermometer frames are manufactured of caoutchouc whale- 

 bone. This material is suitable for this purpose, because it is 

 not warped or cracked by heat or cold like wood, or corroded 

 like metal. They may be immersed in boiling liquids or steam 

 without being injured. 



TELESCOPES. 



The cases of telescopes, opera spy-glasses, and other optical 

 instruments, may be made with advantage of caoutchouc whale- 

 bone or ivory, or being made of sheet metal, they may be im- 

 proved by being enameled with caoutchouc enamel. 



