OF ARTS AND SCIENCES. 71 



tioned at the receiving telephone, which was then placed in a separate 

 room. 



Magnifying powers were used of from 50 to 1,000 diameters. "With 

 the higher powers the use of an objective of short focal length was 

 difficult on account of the small working distance, so that, although 

 even as short a focus as -^jj in. was sometimes employed, it was found 

 much preferable to obtain the needed magnification by the use of short 

 focus eye-pieces. 



The brilliancy of the electric spark was amply sufficient for illumi- 

 nation of the field, even with the highest magnification employed ; a 

 fact which calls attention vividly to the enormous " instantaneous in- 

 tensity " (so to call it) of that light. Considering the excessively brief 

 duration of the spark and the very small quantity of matter illumi- 

 nated, it seems unquestionable that the intrinsic brilliancy is far greater 

 than that of the electric arc, a view fully supported by the results of 

 spectroscopic study. 



Various forms of microphone were observed, but the general fea- 

 tures characterizing the actions studied were common to them all. 

 As the intensity of the sound acting on the microphone was increased 

 by approaching the organ-pipe to the diaphragm, the motion of the 

 hammer electrode, at first absolutely invisible, was seen gradually 

 to increase, until, when the intensity was very great, the motion was 

 excessive, the anvil electrode being violently pushed aside, and the 

 hammer leaving it on its return motion, so that the circuit was broken 

 at every vibration. At the same time bright sparks were seen be- 

 tween the electrodes. To the ear the simultaneous acoustic changes in 

 the sound transmitted were very striking. The sound of the pipe was 

 distinctly audible, and its quality clear, with motions of the hammer 

 electrode far too slight to be observable. As the sound actuating the 

 telephone became louder, and the excursion of the electrode became 

 visible, the quality continued good, the sound transmitted growing 

 louder ; and then, as the excursion increased further, the quality grad- 

 ually changed, shrill false notes made their appearance, and the sound 

 began to grow harsher, until finally, when breaks appeared in the cur- 

 rent, the sound was excessively harsh, and entirely devoid of m.usical 

 quality. Long before this, however, the characteristic quality of the 

 organ-pipe disappeared. 



The following tables will illustrate the results obtained. In mak- 

 ing many of the measurements I worked in company with Mr. W. W. 

 Jacques, whose observations were always in substantial accord with 

 my own. A large number of observations have also been made, under 



