334 RECORD OF SCIENCE FOR 1886. 



than those of other experimenters. This shows that the bicycle or tri- 

 cycle is probably the most economical way of using human muscles. 

 The experiments were made by attaching an indicator diagram appa- 

 ratus to the lever of the safety bicycle known as tlie " Extraonlinary," 

 and also by observing the reduction in speed due to fricion when the 

 bicycle was running free. The experiments also showed that the resist- 

 ance varied almost as the velocity, and that the pressure on the pedal 

 was not constant, but was a maximum at the center of the stroke. 

 (Nature, March, 1886, xxxiii, 455.) 



Curie has contrived a transmission dynamometer having an optical 

 measuring device. An arbor, supported horizontal!}" upon two bearings, 

 carries a pulley at each end, one of Avhich receives the power and the 

 other transmits it to the machine. The power transmitted is deter- 

 mined from the torison of the arbor. This arbor is a metallic tube whose 

 ends are closed by two plates of quartz cut parallel to the optic axis, 

 and each giving a difference of half a wave length between the ordi- 

 nary and extraordinary rays. A beam of polarized monochromatic light 

 traverses the arbor along its axis, the plane of polarization being ro- 

 tated through a definite and invariable angle by the quartz plates. If, 

 however, any torsion of the tube is produced, the plane of polarization is 

 rotated through twice the torsion angle. By a ])reliminary experiment, 

 the couple of torsion necessary to produce a rotation of 1° is determined. 

 Calling this c, and the angle of rotation of the arbor a, the power 

 transmitted per second will be represented by 2, tj, c, a, w, in which 

 n designates the number of revolutions per second. (C. R., July, 1886, 

 cm, 45.) 



MECHANICS. 



1. Of solids. 



Nipher has published a paper on the isodynamic surfaces of the com- 

 pound pendulum. As is well known, certain particles in the system 

 constituting such a j^endulum tend to increase its acceleration, while 

 others tend to diminish it. These two groups of particles are sepa- 

 rated by a surface, such that no particle lying in it has any tendency at 

 a given iiistant to change the acceleration of the system. It is in this 

 surface that the axis of oscillation always lies. On either side of this 

 neutral surface there must exist surfaces of equal tendency — isodynamic 

 surfaces — those on the one side having a plus sign and those on the 

 other a minus sign. Investigation shows these isodynamic lines for a 

 disk i)enclnlum to be concentric circles, their common center being on 

 a horizontal line tlirough the axis of suspension and at a distance from 

 it, depending on the length of the pendulum {i. e., the distance between 

 the axes of suspension and oscillation, respectively), and on the angle 

 of displacement, being half the length of the pendulum when it is 

 horizontal and infinite when it is vertical. These circles are the right 



