350 Prof. J. V. Jones on the Use of Lissajous' Figures 



(i.) The use of Lissajous^ Figures to obtain Equality of Period 

 between the Revolving Apparatus and the Reed. 



In one end of the axle of the revolving apparatus (which in 

 the application of this method in the laboratory of the Uni- 

 versity College, Cardiff, is a Lorenz disk rotating about a 

 horizontal axis) a pin is placed excentrically. The pin fits 

 accurately in a hole in a rod free at one end, and constrained 

 to move only longitudinally at the other. 



Fig. 1 represents an end view of the axle M M M. The 

 excentric pin is indicated by the dotted circle at B. The pin 

 fits into a hole in the rod S S free at the end C, the other end, 

 A, being constrained to move only longitudinally. 



When the apparatus is in rotation the excentric pin im- 

 presses on the rod a vibratory motion; and the vibration- 

 period of the rod is equal to the revolution-period of the 

 revolving disk. 



To the free end of the rod a mirror, T, is attached. 



In the apparatus in my laboratory, already mentioned, the 

 axle is horizontal and the rod moves in a vertical plane. 



The reed is a steel bar 100 centim. long, and its section is 

 rectangular, 1'51 centim. by '60 centim. It is clamped in a 

 massive iron frame, and by moving the bar in the frame the 

 vibrating segment may be made longer or shorter so as to 

 vary its vibration-period. The period may be further adjusted 

 by the movement of a rider. 



Fig. 2 is a plan of the reed and its electrical arrangements, 

 which are a little different to those in ordinary use in order to 

 allow, without inconvenient readjustment of the springs, the 

 lengthening or shortening of the vibrating segment. 



A A A is the steel bar. 



C C the iron frame to which it is clamped by the bolts and 

 nuts D, D. This stand is clamped to a large wooden 

 block resting on a concrete floor. 



F F F is a wooden piece attached at N N to the iron frame, 

 and bearing the electromagnet M. 



On the opposite side of the vibrating bar to the electro- 

 magnet there is a pair of springs Si. One of the pair is 

 always in contact with the bar as it vibrates, and the other, 

 fitted with screw-adjustment, makes and breaks contact with 

 the first. The first spring is connected through the electro- 

 magnet with the pole of a suitable battery, the other pole 

 being connected with the second spring. The apparatus gives 

 no trouble, and once started the reed will vibrate for hours 

 without attention. 



To the free end of the vibrating segment a mirror T T is 



