586 HENRY A. EOWLAND 



focus, showing, provisionally at least, that there was some regular reflec- 

 tion. But these experiments should all be repeated many times before 

 one actually believes them. We don't always believe what we read. 



Now, as to Helmholtz's theory of the motion of ether and so on 

 well, as I said before, what is the motion of the ether? What is motion 

 of the whole ether? You cannot move the ether in the whole universe 

 all at once, and if you do not move the ether in the whole universe 

 all at once but only move a part, then it is a wave, so it amounts to the 

 theory that I gave an impulse, such as Stokes had. Now, an impulse 

 such as Stokes had does not go in a straight line it goes around cor- 

 ners and it does not go in. a straight line unless there are lots of 

 waves coming out. We can readily prove that an ordinary molecule, 

 vibrating to ordinary light, must give out a hundred thousand waves 

 without much diminution of amplitude, or else you cannot have the 

 sharp lines in the spectrum that we do. The molecule must vibrate a 

 long time longer than any bell that we can make. We cannot find a 

 bell that will give out a hundred thousand vibrations without much 

 diminution. For ethereal waves something must vibrate to produce 

 them. What it is I don't know that there is any necessity for discuss- 

 ing, because you can discuss it forever and never get any nearer to it. 

 Something vibrates. Now, the thing that vibrates we don't know. We 

 don't know whether it is electricity or whether it is mechanical motion. 

 We know nothing about it. I have often said to my students, when I 

 showed them the spectrum of some substance like uranium, in which 

 we were taking photographs which would be perhaps ten feet long so 

 fine in grain that you could not put the point of a pencil on it without 

 finding a line. There were thousands of lines. I said to them: " A 

 molecule of matter is more complicated a great deal than a piano. 

 Counting the overtones and everything, you would not probably get up 

 anywhere near the number of tones you get out of a single molecule of 

 uranium. Therefore it rather looks as if the uranium molecule was 

 very complicated." Of course, all those spectrum lines do not indicate 

 fundamental tones many are harmonics. Still it is rather a compli- 

 cated thing to get a spectrum in which there are many thousands of 

 lines. So when I come to think what a molecule is and try to get up 

 some theory of it, I quite agree with Dr. Pupin that we don't know any- 

 thing about it. 



