30 



HENKY A. ROWLAND 



conflicting pulls with no seeming regularity, but each of the balls 5, 

 6 and 8 will pick out from the confused motion the vibration due to 

 itself, and will move in unison, but No. 7 will remain quiet. The short 

 pendulums always produce the effect sooner than the long ones. To 

 remedy this to some extent it is well to bend the wire A into the shape 

 shown in the figure. It is not well to make the pendulum more than 

 twenty inches long, if a quick response is wished. There seems to be 

 no limit to the number of pendulums which can be used or the distance 

 to which the effect can be transmitted, though it is more decided when 

 there are but few pendulums and they are near together. It may some- 

 times be more convenient to suspend the pendulums from a wire, 



:wm 



tightly stretched, than from a board. To make the balls visible at a 

 distance, it may be well in some cases to make them of polished steel, 

 and illuminate them by a beam from the electric lamp. 



These experiments have many advantages which recommend them to 

 teachers; they can be performed without purchased apparatus, and 

 can be made to illustrate resonance and the kindred phenomena in all 

 their details. Indeed, any one will be well repaid for spending an hour 

 in performing them, simply for their own beauty. 



