CHARLES AUGUSTIN COULOMB 151 



its length, and independent of the load on the wire. This 

 was the result of an investigation published in the year 1784, 

 and important in itself in regard to the knowledge of the 

 elastic properties of matter. An interesting point in it was 

 also the method for measuring the force of which he made 

 use. He allowed a body suspended by the wire to execute 

 torsional oscillations about the wire as axis, and measured 

 the period of oscillation with different moments of inertia of 

 the suspended body, from which the elastic force governing 

 the oscillations can be calculated. This was a new applica- 

 tion, the first of its kind, of Huygens' and Newton's investi- 

 gations of the pendulum, to the measurement of forces other 

 than that of gravity. Coulomb further applied this measure- 

 ment of force by means of oscillations (dynamic measurement 

 of force as opposed to static measurement with the torsion 

 balance) in numerous experiments, directly to the measure- 

 ment of electric and magnetic forces. The first to follow 

 him in this method of measuring force and also in the 

 application of the torsion balance, was Cavendish, who 

 applied it in his important investigation of gravitation. 



Coulomb was also active in other directions. He com- 

 pletely investigated the simple laws of sliding friction, ac- 

 cording to which it is proportional to the force with which 

 the two bodies are pressed together, and independent of the 

 size of the surface of contact, - as Leonardo had already 

 recognised - and within certain limits independent of the 

 speed of motion, but larger as we approach rest. In one of 

 his last researches (1801), he investigated the internal fric- 

 tion or viscosity of liquids, which Newton had already con- 

 sidered, by means of torsional oscillations, executed by 

 cylinders hung up in the liquid. 



He came of a family of high social position in the south 

 of France, studied mathematics and science in Paris, and 

 then entered the army. In accordance with his tendencies 

 and capabilities, he joined the technical troops. As officer 



