IV. PENDULUMS AND GYROSCOPES. 147 



No. 2 shows that by the describing point of a string which runs over two 

 rollers, two evolutes constantly coining in contact are traced relatively to 

 them, which for this reason are tooth-profiles correctly working together. 



As the same profiles are described when the axes are removed from or 

 brought nearer to each other, it follows that evolute-wheels may alter the 

 distance of their axes, preserving, notwithstanding, correct contact. 



The circles " K" and " K 1 " cut off from the " contact line" a 6, the 

 contact space PP. 



No. 3 shows that at the cycloid toothing, the " contact space " consists of 

 the curves (segments) cut off from the head circles, and that every normal 

 placed on the tooth-profile in the common point of contact of two teeth always 

 passes through the point of contact of the two dividing circles. 



No. 4 evolves spontaneously the circumferential line of the smallest possible 

 space between the profiles. 



53Ob. Model of Weston's Differential Pulley, with 

 weights complete. 



Polytechnic School at Halle, Director Kohlmann. 



IV. PENDULUMS AND GYROSCOPES. 



531. Gyroscope. A mechanical contrivance to exhibit the 

 phenomena of rotation, and to show experiments on the deviation 

 of spherical projectiles. Elliott Brothers. 



532. Foucatilt's Gyroscope. Ordinary model. 



Geneva Association for the Construction of Scientific In- 

 struments. 



532a. Gyroscope, by Foucault. College of France, Paris. 

 532c. Electric Gyroscopes. G. Trouve, Paris. 



Illustrating trials concerning the maintenance by means of electricity of the 

 motion of the " Foucault " gyroscope. (Solution of the problem of gyroscopy, 

 laid before the inventor by M. Foucault in 1864.) 



533. Polytrope. A gyroscope mounted on circles so as to 

 prove the laws of combined rotations about several axes. It may 

 be used to determine the meridian or the latitude of a place, and 

 to show the rotation of the earth on its axis, and for other 

 experiments. The Council of King's College, London. 



534. " Soldier Experiment." Model designed to demon - 

 strate the relative effects of revolution and of rotation, separate or 

 combined, by the movements of soldiers. Henry Perigal. 



535. Compass Experiment, demonstrating that a mag- 

 netised needle does, but an unmagnetised needle does not, maintain 

 its parallelism while revolving in a circle. Henry Perigal. 



