268 EIGHTEENTH CENTURY. PT. m. 



and the wall this is called a whole wave. By the time 

 this wave has reached the wall at <?, the end of the rope in 

 your hand will have begun to form the trough, #, g, c. 

 Now notice what happens the reflected wave from e 

 travels back along e, d, c, and meets there the new direct 

 wave, a, g, c, coming from your hand. Therefore, at the 

 point c, these two movements will meet, and while the 

 direct wave a, g, c, will be wanting to pull the string up to 

 make its next crest c, d, e, the returning wave e, d, c, will 

 be wanting to pull it down to make its next trough, <:, g, a ; 

 therefore, at this point the string will remain almost at rest, 

 forming what is called a node or knot 



Once past this point, each wave can go on its way, and 

 the string will gradually assume the form a, g, c, d, e. In 

 this way the vibration will continue in two divisions or 

 segments with a. node or point of comparative rest <r, between 

 them. It is not at all necessary that there should be only 

 one point of rest in the string ; by moving your hand more 

 quickly you can make two nodes and three segments as in 

 No. 3, and these may be increased almost indefinitely. 



Now it is an action almost exactly the same as this 

 which takes place in the stretched string of a musical instru- 

 ment when it is made to vibrate. By holding the feather 

 against the string at b, Fig. 48, and thus checking at this 

 point the swing of the entire string you formed a node, and 

 the vibration caused by the scraping of the violin bow instead 

 of having its crest in the middle of the string, had it between 

 a and b. This caused the trough to come between b and c, 

 and the next crest between c and d. Then the reflected 

 wave from d had the same effect as in your swinging rope, 

 No. 3, Fig. 49, and in consequence the string was divided into 

 three segments with two nodes, b and c. When once this 

 vibration is set up, you may remove the feather altogether, 



