ON THE STRUCTURE OF ATOMS. 83 



within the limits of luminiferous vibrations. Hence we have the 

 law of Angstrom, that a gas when luminous emits rajs of light 

 of the same refrangibility as those which it has the power to 

 absorb. 



Heat, which is a vibrating movement of greater amplitude 

 than light, affects the individual atom, not in its parts like light, 

 but as a whole, as will be seen from the following remarkable 

 property of substances, known as specific heat. In all substances 

 whether solid, liquid, or gaseous, a given quantity of heat will 

 raise the temperature of an equal number of atoms or molecules 

 the same number of degrees. Thus 9 Ibs. of water, 56 Ibs. of 

 iron, 118 Ibs. of tin, 200 Ibs. of mercury, warmed by the same 

 amount of heat, would each cause the thermometer to rise exactly 

 the same number of degrees. These numbers, as is well known, 

 represent the relative weights of the molecules or atoms of these 

 several substances, and of course the quantities given above must 

 contain each the same number of molecules. Therefore the 

 mode of motion, or the force, which we call heat affects all 

 molecules or atoms alike, no matter how light or how heavy they 

 may be. Now it is contrary to all the laws that we know of, for 

 a force to move a heavy body as easily as a light one. Conse- 

 quently we must suppose the atoms to be constructed on entirely 

 different principles from ordinary aggregations of matter. It is 

 probable that motion, perhaps the vortex motion of minute por- 

 tions of the ethereal fluid of space, is all we can predicate of 

 them. 



In all substances, simple or compound, there is a degree of 

 temperature at which the particles are suddenly released from all 

 cohesive attraction, and at once have a tendency to fly away from 

 each other. This is at the transition from a liquid to a gaseous 

 state, and the degree of heat at which this change is operated is 

 called the boiling point of each substance. At this point there 

 is a change in the balance of the forces lodged in the molecule 

 they now repel instead of attracting each other. The changes 

 must be in the forces inherent in the particles themselves, for 

 all we have done by the increase of heat is to remove them a 

 little further apart, when all at once they burst away and endeavor 



