physics. L73 



dicular to the shaft, carry pulleys, on each of which winds a cord attached 

 to a cross-bar, fastened at its middle point to a spiral spring within 

 the shaft. If the second and third main pulleys do not move together, 

 the cross-head is moved forward, stretching' the spring and moving an 

 index attached to a rod running through the shaft. To this rod any 

 suitable integrator may be attached. Subsequently, Smith Las pro- 

 posed to show by inspection the rate at which energy is being trans- 

 mitted, by means of two cross-wires perpendicular to each other, one 

 of which, moving horizontally, indicates the tension on the belt in 

 pounds, while the other, moving vertically, shows the velocity at any 

 instant, in feet per second. The point of intersection of these wires 

 would represeut, on a suitable scale, the number of foot-pounds which 

 is being transmitted per second. (Phil. Mag., February, June, 1883, 

 XV, 87, 431.) 



Paquet has devised a simple apparatus for illustrating the laws of 

 free fall under the action of gravity. Two weights are allowed to fall 

 freely between vertical wires. One of these, being started first, falls 

 for a time t and then reaches and releases the second. A stage, as 

 much below the second weight as -this is below the starting point of the 

 first, arrests this second weight after a second time /. If now a second 

 stage be so adjusted as to stop the first weight at the same instant, it 

 will be found that this weight has fallen exactly 4 times as far in 2 sec- 

 onds as the first has in 1. If the stage be placed below the second 

 weight at one-quarter of the distance which this weight is below the first, 

 and this experiment is repeated, it will be seen that in thrice the time 

 the first weight has fallen over 9 times the distance. {Jour. Phys., May, 

 1883, II, II, 226.) 



B^quie" has suggested placing a metallic point on the axis of the pulley 

 of the Atwood machine, so that at each revolution it should touch a 

 mercury surface and close the circuit of a Morse register, thus record- 

 pig the velocities. (Jour. Phys., July, 1883 ; II, n, 323.) 



Gilbert has described a modification of Foucault's gyroscope for show- 

 ing the earth's rotation. It consists, like the gyroscope, of a heavy 

 revolving disk mounted in a frame. But the frame is supported on 

 delicate knife-edges, the axis of rotation being vertical, and the whole 

 is adjusted so that the center of gravity is on the axis of suspension. 

 By means of a small weight, movable in the prolongation of the axis of 

 the disk, the center of gravity could be lowered slightly so as to oscil- 

 late like a pendulum about the knife edges. If now the disk be revolved 

 150 to 200 times a second, and the frame be placed on the knife edges, 

 the line joining them being in the plane of the meridian, the axis of 

 rotation is displaced from the vertical to one side or the other according 

 to the direction of rotation. The results agree with theory. ( Jour. Phys., 

 March, 1883, II, II, 101.) 



Bosanquet has proposed a simple mode of dividing inch and meter 



