1918] Vibrations: IVIechanical, Musical, and Electrical 243 



WEEKLY EVENING MEETING, 



Friday, March 8, 1918. 



The Riciht Hon. Lord RAYLEian, O.M. LL.D. D.8c. F.R.S., 

 in the Chair. 



Professor Edwin H. Barton, D.Sc. F.R.S. 

 Vibrations: Mechanical, Musical, and Electrical. 



I. — Introductory Survey. 



The subject of vibrations is a large one. It comprises a great 

 variety of to-and-fro motions, and these may be executed by diverse 

 systems at widely differing rates. Near one border of the subject 

 lie phenomena so simple that a child may grasp their leading features. 

 Near the opposite border there are phenomena of exceeding com- 

 plexity and their full solution is still awaited. 



It thus appe.irs that parts of the suljject are too elementary and 

 familiar for detailed treatment here, while others may be not yet 

 ripe for general description. But Ijetween these extremes there are 

 portions or aspects of the subject that may prove l)oth interesting 

 and practicable. 



To indicate and locate a few such portions a brief survey of the 

 subject was then taken. Many ways of classifying vibrations are 

 available. But, without aiming at logical precision, a somewhat 

 rough method was considered convenient. Thus, since a vibration 

 is a to-and-fro motion, the various types of such motions may be 

 placed in columns. Secondly, since these motions are executed by 

 some physical systems, the various systems may be placed in rows or 

 lines. This gives the sub-division shown in Table I. 



Neither the columns nor the rows need stop just where they do 

 in this table. For the subject extends further in each direction. 

 Moreover, each column and row admits of further sub-division. So 

 that the ramitications of the subject are almost beyond enumeration. 

 But, as it is, it serves to locate the portions to which chief attention 

 was directed. These were examples of two or more associated vibra- 

 tions whether forced, coupled or compound. 



II. — FoRCiJD AND Coupled Vibrations. 



Forced and coupled vibrations must be distinguished from each 

 other and from the simplest class of all called free vibrations. To 



