142 LECTURES TO SCIENCE TEACHERS. 



bridges at the end and pegs by which these strings can be 

 strained, either by twisting wrest-pins, or by adding weights. 

 Now adding weights is very much the better plan for 

 experimental purposes, and it was the plan employed by 

 the father of all enharmonic instruments, Col. Perronet 

 Thompson, whose organ is exhibited in the Loan 

 Exhibition and of which I -propose to speak to-morrow. 

 Weights have a great advantage in a monochord, because 

 the raising of the note of the string is not in simple 

 ratio to the weights you add, but in that of their square. 

 For instance, if I load the string with a certain weight, two 

 of these separate blocks, and then add two more, I do not 

 raise it to its octave or anything like it. The advantage is 

 that accidental variation in the stretching weight causes only 

 a comparatively small error. A monochord of this kind 

 was used by Perronet Thompson for tuning the pipes of his 

 enharmonic organ. He chose stouter wire and very heavy 

 weights, sometimes more than 250 Ibs. since the best steel wire 

 will stand that weight ; against the notes so produced he cut 

 the pipes of his organ the right length by getting unison. 



Some considerable time ago, an ingenious gentleman of the 

 name of Griesbach carried this contrivance of the monochord 

 still further. He not only measured the ratios of tones but 

 contrived a method of drawing and printing them ; this in- 

 strument we have in the Exhibition. We have also several 

 smaller monochords of Mr. Griesbach's. Here is one with a 

 scale of aliquot parts very elaborately made to measure. 

 Here is a string with fixed points upon it by which the 

 tempered scale of the octave can be accurately obtained. It 

 is an independent reproduction of Broderip's instrument. I 

 wish to call your attention particularly to this large instrument. 

 It has a double-bass string, stretched along this bar of wood, 

 with a sounding-box, and there is a means of tightening it by 

 a screw. Here is a very ingenious rotating bow ; somewhat 

 damaged by time, but of which the principle can still be 

 seen. A piece of vulcanized Indiarubber is covered with 

 horsehair and then, being passed by means of rollers over 

 the string, it gets rid of the great difficulty experienced in 

 using strings for tuning, namely, the evanescence of their 

 tone. It is curious to see later discoveries anticipated 

 by an ingenious man whose labours have been somewhat 

 overlooked. He did more - } here again anticipating modern 



