66 Royal Society : — 



Vibrations. Vibrations. Vibrations. 



Subsidence from 40 initial am- } nf . ~ A c A 



plitudeto20 j 56 64 64 



And from 20 (in course of the \ qfi g q fi 



same experiments) to 10 . . J 

 The same wire and same vibrator showed — 



Subsidence from 20 initial amplitude to 10 ) , , ., . . 



(average of four trials) . ., j U2 Orations. 



Again the same wire with vibrator No. 2* (time of vibration one 

 way 1-236), showed in two trials— Vibrations. Vibrations. 



Subsidence from 40 initial amplitude ) 54 52 



to 20 J 



And continued from 20 to 10 . . 90 90 



Again same wire and vibrator, — 



From initial amplitude 20 to 10. . 103 vibrations (mean of eight 

 trials). 



This remarkable result suggested the question (d). 

 (d) Only one comparison was made. It showed in a wire which 

 was kept vibrating nearly all day, from day to day, after several 

 days, very much more molecular friction than in another kept 

 quiescent except during each experiment. Thus two equal and 

 similar pieces of wire were put up about the 26th of April, hang- 

 ing with equal and similar lead weights, the tops and bottoms of 

 the two wires being similarly fixed by soldering. No. 2 was more 

 frequently vibrated than No. 1 for a few days at first, but no com- 

 parison of viscosities was made till May 15. Then 



No. 1 subsided from 20 initial range to 10 in 97 vibrations. 

 No. 2, the same subsidence in 77 vibrations. 

 During the greater part of May 16 and 17, No. 2 was kept vibrating, 

 and No. 1 quiescent, and late on May 17 experiments with the follow- 

 ing results were made : — Time per 



vibration. 



No. 1. Subsided from 20 to 10 after 99 vibrations in 237 seconds 2*4 



98 „ 235 „ 2-4 



98 „ 235 „ 2-4 



No. 2. Subsided from 20 to 10 after 58 „ 142 „ 2-45 



60 „ 147 „ 2-45 



57 „ .139 „ 2-45 



60 „ 147 „ 2-45 



[Addition, May 27, since the reading of the paper.] — No. 1 has 

 been kept at rest from May ] 7, while No. 2 has been kept oscilla- 

 ting more or less every day, till yesterday, May 26, when both were 

 oscillated, with the following results : — Time per 



vibration. 

 No. 1. Subsided from 20 to 10 after 100 vibrations in 242 seconds... 2-42 

 „ 2. „ „ 44 or 45 vibrations 2*495 



Moduli of Elasticity. — A modulus of elasticity is the number by 



which the amount of any specified stress, or component of a stress, 



must be divided to find the strain, or any stated component of the 



strain, which it produces. Thus the cubic compressibility of water 



* Of same weight as No. 1, but different moment of inertia. 



