1853] WRITINGS OF JOSEPH HENRY. 313 



quiescent. In this state let the engineer enter the tender 

 and touch the valve ; the machine instantly becomes instinct 

 with life and volition ; it has now a soul to govern its power 

 and direct its operations; and indeed as a whole it may be 

 considered as an enormous animal, of which the wheels and 

 other parts are additions to the body of the engineer. 



The facts I have given as to the source of power and its 

 application rest upon the widest and best-established induc- 

 tions of physical science, and a knowledge of them is abso- 

 lutely essential to every one who desires to improve the art 

 of applying the powers of the elements to useful purposes. 

 And yet, — if we are to judge from the constant announce- 

 ment in the papers of new motors, of machines moved by 

 centrifugal force, of engines to do a large amount of work 

 with the expenditure of an infinitesimal quantity of power, 

 of contrivances by which electricity is to develop itself and 

 do work by its own force, — we shall be convinced that on 

 projects which are in opposition to the best-established truths 

 of science hundreds of thousands of dollars are squandered 

 and years of thought and lab^r wasted. One cause of error 

 of this kind is the unfortunate name which was originally 

 given to, and is still retained by, certain elementary ma- 

 chines, viz., the lever, the wheel and axle, the inclined plane, 

 the pulley, and the screw. These are employed separately 

 as instruments for the application of power, or in combina- 

 tion as the elementary parts of complex machines. Every 

 tyro in science knows that they have no power in themselves, 

 yet the name, mechanical powers,hy which they are designated 

 tends to perpetuate a pernicious error long after the fallacy 

 is understood. 



A machine, as I have before stated, is an instrument to 

 apply and modify power, and to effect changes in the form 

 and texture of matter denominated work. The combination 

 of the elementary parts of machines so as to produce any 

 desired motions has been studied with much success, and the 

 whole reduced to rules. The diffusion of a general knowl- 

 edge of these would much facilitate invention and prevent 

 the necessity of the individual who devotes his mind to the 



