FISH-NET PRESEKVATIVES. 



21 



vertical position over e, to a convenient point, d; that is, so that the 

 penduhim when released will swing through an angle. As the 

 pendulum swings it bends the twhie back and forth. The bending 

 of the twine is work and causes the energy originally imparted to 

 the plummet to diminish; that is, the oscillations of the pendulum 

 are of dimmislung amplitude. Presently the pendulum will be 

 swiii^mg only to some selected point, /, as its highest point. If the 

 oscillations from the start are counted until the pendulum swings 

 only to point/, the number will be a measure of the energy that has 

 been transformed m bendmg the line — the more flexible the sample 

 the greater the number of oscillations necessary to reduce the ampli- 

 tude to the predetermined angle. 



For the present work the followuig arbitrary standards were 

 adopted as convenient and easily measured: Distance from jaws 

 to arc base, 30 cm.; weight of plummet 50 g.; angle of first oscilla- 

 tion, one radian (57.2958°, or 

 57°17'45") or 15 cm. of arc from 

 the vertical position to the start- 

 mg point, d; angle of last oscilla- 

 tion one-half radian (28.6479° or 

 28°38'52.5f). All the data on 

 flexibility m this paper are ob- 

 tained on these standards. They 

 are convenient and satisfactory, 

 though there are some grounds 

 for consideruig a smaller angle 

 of oscillation as a possible im- 

 provement. The instrument 

 used m our tests is shown in 

 Figure 8. In the present work 

 the results have been expressed 

 by the number of oscillations 

 necessary to reduce the ampli- 

 tude by the amount chosen, one-half radian. The actual amount of 

 energy may be calculated in the following way: 



When the 50-gram plummet is elevated from C to G, Figure 10, it re- 

 ceives energy in ergs, equal to its elevation, A C, times its mass, in 

 grams, times the force of gravitation. When its amplitude has been 

 reduced so that it rises only to I) on its upward swing, it possesses 

 energy expressed in the same way, only with the lesser elevation, BC; 

 that is, the number of ergs of energy that have disappeared in bend- 

 ing the twine is equal to the difference in elevation times mass, times 

 gravitation, or. 



Energy consumed = {OB - OA) X 50 X 980 



to determine OB — OA we determine OB as r cos y where r is the 

 radius of the circle and y is one-fourth radian, or 14.3239° = 29.07 and 

 OA as r cos x, where x is one-haK radian, or 28.6479° = 26.33. The 

 difference here is therefore 29.07 — 26.33 = 2.74 cm. and the energy that 

 has disappeared is 2.74x50x980 = 134,260 ergs. This quantity, 

 being always the same for the different samples as long as we main- 

 tain the same standards, we have but to divide it by the number of 

 oscillations to find the average amount of energy transformed in bend- 



FiG. 10. 



