Prof. R. R. Ramsey on an Atomic Model. 207 



Note added on the 23rd of December. 



1. The experimental work for the cases in which C x and C 2 

 are of the same sign and of various magnitudes, has since 

 been completed and wall be described in the third paper of 

 this series shortly to be published. The results obtained have 

 an important application in the theory of the Cyclical forms 

 of vibration of a bowed string which may be obtained under 

 a very wide variety of conditions, of which the phenomenon 

 noticed at the " wolf-note " pitch forms only one example 

 (Phil. Mag. October 1916, p. 395). 



2. In the paper on the " wolf-note" just cited, in parag. (c) 

 on page 395, for the word " A-string" read " D-string." 

 Further work has shown that the possibility of a " cyclical " 

 vibration depends not so much on the length of the string as 

 on its frequency. On the D-string of the 'cello I use, 

 eyclical vibrations may be obtained by suitable bowing over 

 a very wide range of frequencies, from 160 to 180 vibrations 

 per second, from 230 to 370 vibrations per second, and even 

 at higher frequencies. Though cyclical forms are usually 

 obtained only when the bow is applied near one end of the 

 string, they may also be noticed under favourable conditions 

 when the bow is applied not far from some important node, 

 e. g., near the point of bisection or trisection of the string. 

 It has also been noticed that in certain cases a periodic (not 

 cyclical) vibration maj be maintained, the frequency of which 

 is not independent of the speed, pressure, or place of bowing. 



XVII. An Atomic Model. By R. R. Ramsey, Ph.D., Asso- 

 ciate Professor of Physics, Indiana University, Bloomington, 

 lnd., U.S.A.* 



MODERN theories of the structure of an atom assume 

 one or more electrons in motion about a central body 

 or positive nucleus. Probably the experiment which has 

 been the most helpful in giving an idea as to the structure 

 of an atom is the Mayer | experiment of the floating needles. 

 This, together with the work of J. J. Thomson J, has become 

 almost classic. 



The experiment gives an idea of the possible structure of 

 atoms, and may account for the periodic variations of the 

 properties of the atoms. Thus one, by assuming that an 

 atom of large atomic weight has more electrons than one of 



* Communicated "by the Author. 



f ' Scientific American,' Supplement, vol. v. p. 2045, June 22, 1878. 



X ' The Corpuscular Theory of Matter,' p. 107. 



