EXPERIMENTS ON TRANSMISSION OF SOUND. 



335 



In the middle of each board a hole is made, 2 or 3 mm wide, the 

 end of the wire drawn through it, wound round a piece of brass or 

 iron wire, about 3 cm long and 2 mm thick, and the end twisted round 

 the straight portion of the thin wire. If the communication is made 

 by cord, the ends are tied firmly round the crosspieces. The sound- 



10. 211 (A, an. proj. i real size ; B, twice real size ; C. an. proj. ~ real size}. 



ff-boards, or sounding-boxes, as they might be called on account of 

 e frames, should be placed with the frames turned towards one 

 Bother, the crosspieces of stouter wire being on the free sides which 

 3 turned away from each other. 



f the experiments are made with twine of not more than 100 m in 

 'igth, the two observers may simply each hold one of the boxes 



