﻿1G Mr. C. \ . Raman on Mot 



ion in a 



may be any one of a descending series of sub-multiples of 

 the frequency of the field. It appears, in fact, that we have 

 here an entirely new class of resonance-vibrations. It will 

 be noticed that if the two series referred to above are both 

 written in the same order of descending magnitudes of 

 frequency, thus, 



.6. 5 4 3 2 1 

 2> 2» 2' 2> 2' 2' 



_t 1 1 1 1 _L 



1> 2> 3' 4> 5' tf> 



the last two terms of the first series, and the first two of the 

 second series coincide, and these two are to some extent 

 typical of the rest. For, as I have shown in a previous 

 publication *, the 1st, the 3rd, the 5th, and the odd types 

 generally in the first series bear a family resemblance to 

 each other, giving symmetrical vibration curves. The 2nd, 

 the 4th, and the other even types similarly resemble each 

 other in giving markedly asymmetrical vibration curves- 

 Since the first term in the ascending series is the 2nd in the 

 descending series, we may expect that the 2nd, 4th, 6th, &c. 

 in the latter would give analogous types of motion, and that 

 similarly the 1st, 3rd, 5th, &c. would show resemblances 

 amongst each other. These points will be dealt with more 

 fully as we proceed. 



The vibrations studied which form the subject of this 

 section were those of the armature-wheel of a synchronous 

 motor of the attracted- iron type, about a position of equi- 

 librium in the magnetic field produced by an intermittent 

 current circulating in the coils of an electromagnet. The 

 phonic wheel or synchronous motor devised by La Cour and 

 Lord Rayleigh is, as is well known, of great service in 

 acoustical investigations. In my own work on vibrations 

 and their maintenance, it has been of considerable assistance. 

 Apart, however, from the various uses of the instrument in 

 different branches of Physics and in Applied Electricity, it 

 possesses much intrinsic interest of its own as an excellent 

 illustration of the dynamics of a system moving in a periodic 

 field o£ force, and the present paper deals almost entirely 

 with experiments carried out by its aid and with its applica- 

 tions to the study of vibrations. 



The instrument used by me was supplied by Messrs. Pye 

 & Co., of Cambridge, and has given entire satisfaction. The 

 motor consists of a wheel of soft iron mounted on an axis 

 with ball-bearings between the two poles o£ an electromagnet 

 placed diametrically with respect to it. The wheel has thirty 



* See Physical Review, Dec. 1912. 



