PRINCIPLES OF THE MECHAOTCAL THEORY OF HEAT. 



By Dr. Joii. Muller, 

 Trofessor of Physics in the University of Freiburg, in Berne. 



[communicated by the author, in GERMAN, TO THE SMITHSONIAN INSTITUTION, FROM HIS LEHRBUCH 

 DER PHYSIK, AND ACCOMPANIED BY HIS ALTERATIONS AND CORRECTIONS.] 



I. DEVBLOPMEJfT OF HEAT BY MECHANICAL MEANS. 



It is well known that by compression of the air heat is disengaged; and under 

 certain circumstances, as, for example, by means of the fire syringe, may be ren- 

 dered so considerable as readily to kindle combustible matter. Such develop- 

 ment of heat, however, also takes place through the compression of a solid body. 

 To how high a degree the hardest bodies may be heated by violent compres- 

 sion may be observed in the hammering of metals and the coining of money. 



But among all mechanical means of generating heat none is more available 

 than friction ; and it is this which is almost universally employed Avhen fire is 

 to be provided anew. Every one knows that, for this purpose, uncivilized tribes 

 make use of two pieces of wood — Fig. 1, for example, shows an arrangement of 

 which the Dakota Indians avail themselves. A staff, a h, of hard wood, about 



Fig. 1. 



six inches long and somewhat sharpened at both ends, is inserted i)i a small 

 cavity of the board A, is press(.'d on the upper end by the board B, and, in the 

 manner represented in the figiu-e, is thrown into rapid revolution. As soon as 

 fire makes its appearance, a piece; of tinder, applied by a second person, efiects 

 the desired i)urpose. The kindling of fire by steel and Hint depends likewise 

 on the application of heat, developed- by attrition, which suffices to kindle to a 

 glow Some of the small detached particles of steel, and the now widely-employed 



