60 HEAT OR CALORIC. 



For medical and chemical purposes, the bulb should be naked, 

 with a part of the tube projecting below the scale. 



It has important uses to a gardener, as in observing the temperature 

 in hot houses, and the heat adapted to sowing and planting. 



It is useful at sea, as in the gulf stream where the water is warmer 

 than the mean ; also in approaching land, and in coming on soundings 

 or shoals, and near icebergs, where the temperature always changes 

 and grows colder.* 



It is important to travellers in observing climates ; to many artists 

 in regulating their processes, and to all persons in observing the weath- 

 er, and in regulating the heat in their apartments, in baths, &tc. 



(t.) Varieties of thermometers. The principal are the self-re- 

 gistering, of which Six's is the most remarkable; the air, the spirit, 

 the water, and the mercurial thermometer. Wollaston's for measur- 

 ing heights, is a very delicate instrument, which will be mentioned 

 again. 



Thermometers are made of various form and graduation, sometimes 

 with glass scales for immersion in acids, with naked balls, &tc. They 

 are often in pendent boxes, or in cases which shut for travelling. 



Laboratory thermometer. 



" The thermometers used in laboratories, are 

 usually constructed so as to have a portion of the 

 wood, or metal, which defends them from inju- 

 ry, and receives the graduation, to move upon a 

 hinge, as in the accompanying figure. 



" This enables the operator to plunge the bulb 

 into fluids, without introducing the wood or met- 

 al, which would often 'be detrimental either to 

 the process or to the instrument, if not to both. 



" The scale is kept straight, by a little bolt on 

 the back of it, when the thermometer is not in 

 use." Dr. Hare. 



o 



* The thermometer is regularly used on board of ships of war, and its indications 

 are recorded once or twice a day. Not only does the water always grow colder or 

 coming upon soundings, but generally the air grows colder as we approach land. 

 (See Dr. John Davy's observations in the Journals.) 



