794 HEAT-REGULATOR 



Dr. Joule has clearly shown, that whatever may be the source of heat, a certain 

 fixed elevation of temperature is produced by a given amount of mechanical, chemical, 

 electrical, or vital disturbance, and that the mechanical value of the cause producing 

 the heat is exactly represented by the mechanical effect obtained. 



For a full discussion of this important point, see the Memoirs of Joule, of Thomson, 

 and of Rankine, in the ' Philosophical Transactions ' of London and Edinburgh. The 

 applications of heat will be found under the proper heads. The reader should also con- 

 sult the article HEAT in Watts's 'Dictionary of Chemistry.' See also SPHEROIDAL STATE. 

 HEAT-REGULATOR, or THERMOSTAT. The name given by M. Bonnemain to 

 an ingenious apparatus for regulating the temperature of his incubating stove-rooms. 

 See INCUBATIOX, ARTIFICIAL, for the manner of applying the Heat-Regulator. 



The construction of the regulator is founded upon the unequal distillation of different 

 metals by the same degree of heat. A rod of iron x, fig. 1143, is tapped at its lower 

 end into a brass nut y, enclosed in a leaded box or tube, terminated above by a brass 

 collet z. This tube is plunged into the water of the boiler, alongside of the smoke- 

 pipe. Fig. 1144, is a bird's-eye view of the dial, &c. The expansion of the lead 

 being more than the iron for a like degree of temperature, and the rod enclosed within 

 the tube being less easily warmed, whenever the heat rises to the desired pitch, the 

 elongation of the tube puts the collet z in contact with the heel, a, of the bent lever 

 a, b, d; thence the slightest increase of heat lengthens the tube anew, and the collet 

 lifting the heel of the lever, depresses the other end d through a much greater space, 

 on account of the relative lengths of its legs. This movement operates near the axis 

 of a balance-bar e, sinks one end of this, and thereby increases the extent of the move- 

 ment, which is transmitted directly to the iron skewer v. This, pushing down a swing- 

 register, diminishes or cuts off the access of air to the fire-place. The combustion is 

 thereby obstructed, and the temperature falling by degrees, the tube shrinks and 



disengages the heel of the lever. 

 The counterpoise g, fixed to the 

 balance-beam e, raises the other 

 extremity of this beam by raising 

 the end, d, of the lever as much 

 as is necessary to make the heel 

 bear upon the collet of the tube. 

 The swing-register acted upon 

 by this means presents a greater 

 section to the passage of the 

 air ; whence the combustion is 

 increased. To counterbalance 

 the effect of atmospheric changes, 

 the iron stem which supports 

 the regulator is terminated by a 

 dial disc, round the shaft of the 

 needle above h, fig. 1144; on 

 turning this needle, the stem 

 below it turns, as well as a screw at its under end, which raises or lowers the leaden 

 tube. In the first case the heel falls, and opens the swing-register, whence a higher 

 temperature is required to shut it, by the expansion of the tube. We may thus 

 obtain a regularly higher temperature. If, on the contrary, we raise the tube by 

 turning the needle in the other direction, the register presents a smaller opening, 

 and shuts at a lower temperature ; in this case we obtain a regularly lower tempe- 

 rature. It is therefore easy, says M. Bonnemain, to determine a priori the degree 

 of temperature to be given to the water circulating in the stove-pipes. In order to 

 facilitate the regulation of the apparatus, he graduated the disc dial, and inscribed 

 upon its top and bottom the words Strong and Weak heat. 



THERMOSTAT, is the name of an apparatus for regulating temperature, in vapori- 

 sation, distillations, heating baths or hothouses, and ventilating apartments, &c. ; 

 for which I obtained a patent in the year 1831. It operates upon the physical prin- 

 ciple, that when two thin metallic bars of different expansibilities are riveted or 

 soldered facewiso together, any change of temperature in them will cause a sensible 

 movement of flexure in the compound bar, to one side or other ; which movement 

 may be made to operate, by the intervention of levers, &c., in any desired degree, 

 upon valves, stopcocks, stove-registers, air-ventilators, &c. ; so as to regulate the 

 temperature of the media in which the said compound bars are placed. Two long 

 rulers, one of steel, and one of hard hammered brass, riveted together, answer very 

 well ; the object being, not simply to indicate, but to control or modify temperature. 

 The following diagrams will illustrate a few out of the numerous applications of this 

 instrument : 



