STRAIN ON THE PHYSICAL PROPERTIES OF MATTER. 
817 
Vjbration-period 
in seconds. 
Observed 
logarithmic 
decrement for one 
vibration. 
Logarithmic 
decrement due to 
the resistance of the 
air. 
Logarithmic 
decrement due to 
internal molecular 
friction. 
Temperature in 
degrees Centigrade. 
1-579 
•020236 
•000913 
•019323 
10’25 
2-362 
•022346 
•000831 
•021515 
10-25 
3-898 
•024343 
•000912 
•023431 
10-25 
The brass cylinders replaced by lead cylinders, so that the total mass of 
the vibrator was 168 grms. 
1-913 
■018784 
•000833 
•017951 
3-40 
4-366 
•023664 
•000535 
•023129 
3-40 
7-989 
•024885 
"000616 
■024239 
3-40 
1-913 
•020533 
■000833 
•019700 
10-25 
4-366 
•026035 
•000535 
•025500 
10-25 
7-989 
•027316 
•000616 
•026700 
10-25 
Remarks on Experiments III-VI. inclusive. 
Let us now see what we can gather from the data given in these experiments. 
With tin the logarithmic decrement decidedly increases with the vibration-period, but 
not in the same proportion as the lafter, and may be expressed by the following 
formula :— 
\ T — a hr ~h ct~', 
where t is the vibration-period and \ T the logarithmic decrement, whilst a, b, and c 
are constants, the last being a negative quantity. Thus, when the mass of the 
vibrator in Experiment VI. was 49 grms., and the temperature 10 o, 25 C. : the formula 
became 
\ T =-012407 + -005437t--0006693t 3 ,.. (9) 
whilst for the same temperature; and with the mass of the vibrator equal to 168 grms., 
it was 
\ T = *012381 + -004466t—-0003347t 3 .(10) 
The logarithmic decrement would thus seem to be capable of being divided into 
two parts, the one being independent of the load and of the vibration-period, and the 
other dependent upon the load and the vibration-period. 
When the mass of the vibrator was 168 grms., and the temperature 3°"40 C., the 
formula became 
MDCCCLXXXVI. 
\ T =-011470 + -0039473 t—*0002925 t 2 
5 M 
( 11 ) 
