330 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



pictures as a thin-lined sine curve. This curve is in phase with the 

 impressed voltage immediately about the crystal, and is referred to be- 

 low as the " voltage-phase curve." 



In tracing all the curves, the motion of the light spot over the paper 

 is from left to right ; the time co-ordinate is, therefore, the abscissa of 

 the curves and is drawn as usual from left to right. 



The scale drawn in ink at the left-hand margin of each picture gives 

 the value of the current, one division being one milliampere. 



A tabular description of the conditions under which each of the 

 records was taken is contained in Table IV. 



TABLE IV. 

 Tabular Description of the Oscillographic Records of the Plate. 



A discussion of the records follows. 



Oscillogram Nos. 1, 2, and 3 — Molybdenite. — The pressure of the 

 copper rod 12 against the molybdenite for good rectification is slight, and 

 is somewhat difficult to attain. Some points of the crystal are more 

 sensitive than others, and the crystal has to be moved around under 

 the copper contact and tried at several different points before the 

 best adjustment can be found. Oscillogram No. 1 was taken with a 

 molybdenite rectifier in good adjustment. The rectification in this 

 case is seen to be practically perfect ; the cycle through the specimen 



12 The end of the copper rod in contact with the molybdenite had an area of 

 4 sq. mm. 



