PIERCE AND EVANS. — CAPACITY OF CARBORUNDUM. 797 



adjustment that happened to give the capacity eflfect in a marked degree. ^ 

 Then without changing the adjustment a complete set of data with dif- 

 ferent speeds and different applied voltages was taken. After the ex- 

 periment was completed, the specimen was examined with a microscope 

 and was explored electrically while under the microscope, and the exis- 

 tence of the conducting laminae separated by insulating sheets was dis- 

 covered. After the discovery of these laminae, other specimens could 

 be selected and, with a somewhat difficult adjustment of the electrodes 

 against the conducting laminae, could be shown to act as condensers 

 with larger capacity in some cases than that of the specimens with which 

 the present data were obtained. 



Data ivith Specimen I. — Table I. following contains values of the 

 charge and discharge current obtained with Specimen I, in a circuit of 

 the form of Figure 1, under various impressed voltages and for various 

 numbers of charges and discharges per second. The crystal was con- 

 nected into the circuit so that one side should be positively charged (see 

 column headed "A positive") and then, without changing the adjust- 

 ment of the specimen in the clamp, the leads to the crystal were re- 

 versed so that it should be charged with the other side positive (see 

 column headed " B positive "). 



Charge and Discharge Current not a Linear Function of the Voltage. 

 — From these data, sample curves of charge and discharge current 

 plotted as a function of the impressed voltage, with n = 24.2, are given, 

 in Figure 3, with the charge applied so that the side A was positive, 

 and in Figure 4 with the charge applied in the opposite direction. Along 

 with the "charge" and "discharge" curves there is plotted, in each 

 figure, a curve of steady current through the crystal obtained when the 

 various voltages were applied directly in circuit with the crystal and 

 galvanometer without the intermediation of the commutator. These 

 curves, which are marked "steady," are the current-voltage character- 

 istics of the crystal in the two opposite directions. 



The curves of Figures 3 and 4 show that the charge and discharge 



^ In his testimony, on May 22, 1911, in the case of the National Electric 

 Signaling Company vs. The United Wireless Telegraph Company, Equity 

 No. 643, District of Maine, Dr. Louis Cohen stated that a certain carborundum 

 detector had a capacity of about .004 microfarads. This result he obtained by 

 measurements with a high frequency generator of 72,500 cycles. So far as we 

 know, his result has not been published except in the Court Record. Dr. Cohen 

 gave no explanation of the phenomenon. 



Our own discovery of the capacity was made before the date of Dr. Cohen's 

 experiments, and our delay in publication has been occasioned by a long and 

 tedious search for the explanation of the phenomenon, which we believe we 

 have now found. 



