NOTES 



A THERMOMETER FOR CLASS ILLUSTRATION, 



For lecture experiments a tliermometer should be sensitive so as 

 to show slight changes of temperature, and should make these 

 changes readily apparent to all in the room — that is, the changes 

 should not only be clearly visible but should be such as are com- 

 monly referred to the action of heat and used for its measurement. 

 The ether thermometer, based on the low temperature at which 

 ether boils, will show only an increase of temperature, and the ig- 

 niting of the vapor does not point directly enough to the change to 

 b9 msasured. So, too, the closing of an electric current by mercury 

 risinsJ^ in a tube, and the breaking of the same by its falling, make 

 the change of temperature very apparent but introduce too many 

 elements of confusion. 



Discarding these forms of thermometers, then, I have been using a 

 modification of the air-thermometer which answers all the require 

 ments. As I have seen no mention of such a thermometer in any 

 of the ordinary books on lecture experiments, I offer a description 

 of it to the Society for the benefit of members who have felt the 

 need of such a thermometer and have failed, as I have, to gain any 

 help from the usual reference books. 



The construction of the thermometer is very simple. 

 A piece of glass tubing 59 — 75 c. m. long and 5 — 10 m. 

 m. wide is sealed at one end and an oblong bulb is 

 then blown on it. This bulb may be larger or smaller 

 according to the substance whose temperature is to 

 measured. The thickness of its walls largely deter- 

 mine its sensitiveness. The tube is then bent four 

 times at right angles as shown in the figure. In the 

 open end a liquid (mercury, colored water or alcohol) 



Ois poured until it rises to any desired level. By prop- 

 erly moving the tube it can be gotten to the same 

 level in both arms of the tube without getting in the 

 bulb. It may be well to keep several such thermometers, contain- 

 ing diilerent liquids, so as to have different degrees of sensitiveness. 



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