PIERCE AND EVANS. — CAPACITY OF CARBORUNDUM. 821 



cernible with one of these random adjustments sensitive to electric 

 waves ; 



3. In rare cases, obtainable only after numerous trials, the adjustment 

 of the contact upon the crystal would give a capacity ; in these cases the 

 system would also act as a detector for electric waves. 



These observations show that the detection of electric waves occurs 

 for practically any conductive high-resistance contact of the electrode 

 with the crystal, whereas only a rarely attainable adj ustment of the con- 

 tact against a conducting stratum that happens to be pretty well insu- 

 lated from the other electrode gives the capacity effect measurable by 

 the method of charge and discharge. It is however apparent that if 

 the capacity measurements could be made with the high frequency 

 oscillations of wireless telegraphy, the capacity effect would appear 

 much more commonly. 



Summary. 



1. An electrostatic capacity is found in carborundum. 



2. The capacity-measurements with two specimens are given for dif- 

 ferent voltage and different frequencies of charge and discharge. The 

 capacity of one of the specimens was about .006 microfarads; that of 

 the other about .022 microfarads. 



3. With Specimen I. a leak, different in different directions of charge 

 and not obeying Ohm's law, made the measurements uncertain of accu- 

 rate interpretation. 



4. Specimen II. was practically non-leaky but showed incompleteness 

 of charge and discharge such as would be obtained with a high resistance 

 (120,000 ohms) in the circuit. A reduction of the observation on the 

 assumption of incomplete charge and discharge gives a capacity, which 

 for voltages not zero, is different in the two opposite directions of 

 charge. In one direction of charge the capacity increases with increase 

 of applied voltage; while in the opposite direction of charge the capacity 

 decreases with increase of voltage. 



5. The existence of capacity in the crystal was found to be due to the 

 existence of numerous alternate conducting and insulating strata within 

 the crystal. These strata are visible with vertical illumination and 

 moderate magnification. 



6. Micrographs showing the stratification are given. 



7. So far as the present experiments show, the action of the carborun- 

 dum as a detector for electric waves and as a rectifier for electric cur- 

 rents is independent of its action as a capacity. But it will detect 

 electric waves or rectify only provided contact is made to one or more of 



