820 PROCEEDINGS OF THE AMERICAN ACADEMY. 



band between the dark lines is the outcrop of an insulating layer sepa- 

 rating the two conducting strata. Thus we have a visible condenser in 

 the specimen. The capacity of this condenser was too small to be 

 measured by the method we were employing, and this specimen is kept 

 for future investigation. 



Micrograph of Specimen I. — The pictures e and / of Plate I. show 

 micrographs of the two opposite sides, respectively, of Specimen I. The 

 electrical connection of the specimen into the test circuit was by means 

 of screws set up against the two sides of the crystal. The ends of the 

 screws were so large that the exact point of contact of the screws against 

 the crystal could not be accurately determined, but one of the screw 

 contacts was apparently against the ridge near the center of e ; the other 

 screw contact was near the center oif, which is opposite to e. Judging 

 from the large value of the capacity obtained, we are of the opinion that 

 more than one conducting dyke was in contact with each electrode, and 

 that we were dealing with a multiple -plate condenser. Of this, however, 

 we cannot at present be certain, as we have not as yet been able to 

 measure the dielectric constant of the insulating strata, and have not 

 yet been able to determine accurately the geometrical dimensions of the 

 crystal condensers. 



Note on Relation of Stratification to Action of Carborundum 

 Crystals as Detectors for Electric Waves. 



Not all points of a carborundum crystal are equally good detectors 

 for the electric waves of wireless telegraphy. After our discovery of the 

 existence of alternate conducting and insulating strata in the carborun- 

 dum crystal, we arranged circuits, with the crystal connected to a mul- 

 tiple-pole switch so that it could be thrown into a wireless telegraph 

 circuit and tested for its sensitiveness to electric waves produced by a 

 test buzzer ; then into a circuit of the form of Figure 1, and tested for 

 conductivity and capacity. 



The crystal was mounted in the field of a microscope and was carried 

 by a mechanical stage with micrometer adjustment so that different 

 parts of the crystal, while under observation with the microscope, could 

 be brought into contact with the pin-point electrode. 



It was found that 



1. The crystal and its contact (i. e. the detector) did not respond to 

 electric waves, and did not conduct, and did not have capacity when the 

 point electrode was on one of the light- colored strata; 



2. The crystal detector did respond whenever the contact was against 

 one of the darker strata. In general, however, no capacity was dis- 



