76 PROCEEDINGS OF THE AMERICAN ACADEMY 



Jones and Dame. The latter series was somewhat more complete than 

 the former,* besides being carried on with better instrumental appli- 

 ances, and the results hereafter given are taken chiefly from it. 



In all experiments of the nature of those under consideration, it is 

 very difficult to get any fixed standard of quality to which to refer 

 such results as the present. Different observers differ to a certain 

 extent in their estimate of the excellence of the quality reproduced. 

 But the point at which the distinctive quality of the transmitted sound 

 disappears is quite well marked, and a very slightly increased vibration 

 of the hammer electrode causes great harshness to result. For this 

 reason, the name " critical point," originally suggested by Mr. Jones, 

 has been given to this limit, and the excursion corresponding to it has 

 been particularly noted, in tests of the varying effects of mass and 

 pressure. 



The transmitter used had its anvil electrode suspended like a pen- 

 dulum, as before. In order to vary the mass without varying the 

 normal pressure, a horizontal wire was suspended beneath the anvil 

 electrode and rigidly attached to it. The middle point of the wire 

 was vertically beneath the point of suspension of the electrode. The 

 masses added consisted of small copper washers weighing 1.1 grams 

 each. By adding two of these whenever the mass was to be in- 

 creased, and placing one on each side of the middle point of the hori- 

 zontal wire, the mass of the electrode was increased, while the normal 

 pressure remained substantially constant. In the experiments whose 

 results are contained in Tables IX. to XIII. the normal pressure 

 was exceedingly small, the electrodes always being kept in very light 

 contact. This condition of things was easily secured by a slight 

 adjustment of the position of the washers. A magnification of 280 

 diameters was usually employed. 



The following results were obtained by the mode of procedure just 

 described. 



TABLE IX. 



