72 PROCEEDINGS OF THE AMERICAN ACADEMY 



my direction, by Messrs. A. W. Jones and F. L. Dame, students in 

 the Laboratory, whose work has been performed with conscientiousness 

 and accuracy. 



The microphone used in most of the experiments was one in which 

 the anvil electrode was a " pendulum electrode," suspended by a ver- 

 tical rod, hinged at the top, and so weighted as to give to it a proper 

 mass. The desired normal pressure could be obtained by sliding the 

 point of suspension laterally so as slightly to incline the supporting 

 rod, and further, by adding a weight so as to exert a proper leverage, 

 if this was desired. The hammer electrode was pointed and carried 

 by the diaphragm, which was of mica. The sounding pipe was grad- 

 ually removed from or approached toward the microphone. Care was 

 in all cases taken to keep the wind pressure constant. A single Le- 

 clanche cell was ordinarily used, though in a few cases a Gr(5net cell 

 was employed. 



In the various tables, the excursions of the electrodes are in all 

 cases given in fractions of an inch. In designating the material of the 

 electrodes, that of the anvil is stated first. 



Tables I. to III. show the results obtained when both electrodes 

 were of carbon ; Tables IV. and V., when the anvil electrode was of 

 carbon, the hammer of platinum. Tables VI. to VIII. contain re- 

 sults of observations made with a modified form of transmitter, in 

 which the anvil electrode was also somewhat heavier than in the 

 earlier experiments. 



TABLE I. 



Electrodes, Cakbon, Carbon. — Magnification, 50 diameters. 

 Excursion, Character of Sound 



1000 X 10-« to 700 X 10-6 Constant breaking and sparks. Elec- 



trodes visibly separating. 

 600 X 10-6 Constant sparking. Electrodes occasion- 



ally seen to separate. 

 200 X 10—6 Occasional breaks and sparks. 



200 X 10-^ Scratchy sound, no sparks. 



No visible motion. Sound clear and smooth. 



TABLE II. 



Electrodes, Carbon, Carbon. — Afagni/ication, 50 diameters. 

 Excursion. Character of Sound. 



1000 X 10-6 to 600 X 10-6 Constant sparks ; electrodes separating. 



300 X 10-6 to 200 X 10-6 Harsh ; occasional breaks and sparks. 



150 X 10-6 Scratchy. 



No visible motion. Clear and smooth. 



