ATOMS AND SUNBEAMS. 125 



second. Such would be the minute anatomy of the diamond. The well- 

 known properties of such gems seem, at first sight, wholly at variance 

 with the curious structure we have assigned to them. Surely, it may be 

 said tbat the hardness and tlie impenetrability so characteristic of the 

 diamond refute at once the supposition that it is no more than a cluster of 

 rapidly moving particles. But the natural philosopher now knows that 

 his explanation of the qualities of the diamond holds the field against 

 all other explanations. The well-known impenetrability of the diamond 

 seems to atinse from the fact that when you try to press a steel point 

 into the stone you fail to do so because the rapidly moving molecules 

 of the gem batter the end of the steel point with such extraordinary 

 vehemence that they refuse to allow it to x)enetrateor even to mark the 

 crystallized surface. When you cut glass with a diamond it is quite 

 true that the edge, which seems so intensely hard, is really composed 

 of rapidly moving atoms. But the glass which is submitted to the 

 operation is also merely a mass of moving molecules, and what seems 

 to happen is that, as the diamond is pressed forward, its several i^arti- 

 cles, by their superior vigor, drive the little particles of glass out of the 

 way. We do not see the actual details of the myriad encounters in 

 which the diamond atoms are victorious over the glassy molecules; we 

 only discern the broad result that the diamond has done its M^ork, and 

 that the glass has been cut. 



It may well be asked how we know that matter is constituted of 

 molecules in intensely rapid movement. The statement seems at the 

 first glance to be so utterly at variance with our ordinary experience 

 that we demand, and rightly demand, some convincing x^roof on the 

 matter. There are many arguments by which the required demon- 

 stration can be forthcoming. The one which I shall give is not i^erhaps 

 the most conclusive, but it has the advantage of being one of the sim- 

 plest and the most readily intelligible. 



Let us see if we can not prove at once that the molecules in, let us 

 say, a piece of iron must be in movement. Suppose that the iron is 

 warmed so that it radiates heat to a perceptible extent. We know 

 that the heat which, in this case, affects our nerves has been trans- 

 mitted from its origin by setherial undulations. Tliose undulations 

 have undoubtedly been set in motion by the iron, and yet the parts 

 of the metal seem quite motionless relatively to each other, notwith- 

 standing that they possess the power of setting the aether into vibra- 

 tion. It is impossible that such vibrations could be i^roduced were it 

 not that there is in the iron a something which vibrates in such a 

 manner as to communicate the necessary pulses to the lether. It 

 therefore follows that in the texture of the solid iron there must be 

 some molecular movement, timed in such a way as to impart to the 

 ffither the actual vibrations which we find it to possess. The argument 

 in this case may be illustrated by the analogous phenomena presented 

 in the case of sound. As we listen to the notes of a violin^ what we 



