310 WRITINGS OP JOSEPH HENRY. [1853 



There can be no reality in science if at this late day it 

 cannot predict that certain proposed inventions are impos- 

 sible, as well as declare that others are in accordance with 

 established principles. An honest expression of opinion on 

 such points, though it be met with the accusation of repress- 

 ing the march of improvement, is necessary in order to save 

 the public from having its attention perpetually distracted 

 by the excitement of fallacious expectations, and the credu- 

 lous from embarking their all in schemes which must end 

 in disappointment and ruin. 



One of the most fruitful sources of error and deception 

 with regard to inventions arises from misconceptions of the 

 nature and application of mechanical power, and this is one 

 of the points on which I wish to arrest your attention for a 

 few minutes. We understand by the term mechanical power 

 that which moves machinery, transports heavy bodies, shapes 

 the raw material into useful forms, and to use the short but 

 expressive phrase of the mechanic, " that which does work." 

 Mechanical power, when properly understood, is a condition 

 or state of matter. Thus a quantity of burning fuel, a mov- 

 ing mass of water or of air, are bodies in the condition of 

 power, and by communicating a portion of their motion to 

 other bodies they produce in them certain changes which are 

 denominated tvork. The change thus produced is the meas- 

 ure of the amount of power in a given quantity of matter. 

 For example, the number of bushels of grain which can be 

 ground during the combustion of a bushel of coal is the 

 measure of the amount of power in this quantity of fuel. 



Power is always expended in doing work, and it is in the 

 highest degree absurd to think of applying it to useful pur- 

 poses without exhausting it. Every change of condition, 

 every transformation of matter, every new motion, and every 

 manifestation of life is at the expense of some motive power 

 which, having performed its part, is forever neutralized. 



Power is always the product of nature. God has not vouch- 

 safed to man the means of its primary creation. It is found 

 in the moving air and the rapid cataract — in the burning 

 coal — the heaving tide ; man transfers it from these to other 



