Polytechnic Association. 777 



diffuse itself in inverse ratio to the square of the distance. So much 

 for the law of gravitation, miscalled a theory, but simply a fact. 



The modern conceptions of heat are a theory. The old theory was 

 that heat is a caloric fluid. That theory is totally exploded, for the 

 simple reason that if there were such a fluid, we could not produce 

 rt ad infinitum. The first man that pointed out that heat can be 

 produced continuously was Count Rumford. In his experiments on 

 friction, he found that he could keep water boiling day after day, and 

 produce any amount of heat. Where did that heat come from ? It 

 was not a fluid, or it would have been exhausted. By the modern 

 theory, it was the power exerted by the friction, which. was changed 

 into heat. Pursuing that idea, Mayer, Joule, Helmholtz, and others, 

 adopted the theory that there is a relation between heat and motion ; 

 that heat is only a mode of motion ; that heat is molecular motion. 

 When the motion of a mass is changed into a motion of the molecules 

 of the mass, the peculiar molecular motion causes all the phenomena 

 of heat. 



Now my hypothesis relates to the character and velocity of that 

 molecular motion. But before I enter upon that, let me explain 

 further the theory of heat. One important point was the adoption 

 of the unit, which is the amount which will raise one pound of water 

 1° Fahrenheit. 



It requires different amounts of heat to raise the temperature of 

 different substances 1°. Three pounds of water require exactly the 

 same amonnt of heat as 100 pounds of mercury, ninety-seven pounds 

 of gold, fifty-four pounds of silver, thirty-two pounds of copper, 

 twenty-eight pounds of iron, or sixteen pounds of sulphur. Or, three 

 pounds of hot water will melt as much ice as 100 pounds of equally 

 hot mercury. It will be observed that, excepting water, the numbers 

 are the chemical equivalents of the substances. Now, if we consider 

 that all the other substances are elementary, and that water is com- 

 posed of three atoms, H. O. H, which raises it to nine, the old chemi- 

 cal equivalent, we see the reason of the exception. 



What does this teach us ? If the chemical theory is correct that 

 atom combines with atom, 100 pounds of mercury contain as many 

 atoms as sixteen pounds of sulphur. It also shows that all simple 

 atoms have the same specific heat, no matter what the substance is. 



Latent heat, which has more direct relation to the hypothesis I have 

 to present, is that which is necessar}' to change a solid into a liquid, 

 a liquid into a gas, or a gas into its elements. Water, in its natural 

 form, without heat, is a solid. It may have any temperature, from 



