PIERCE AND EVANS, — CAPACITY OF CARBORUNDUM. 



817 



decided to make further measurements before entering into an attempt 

 to consider more of the factors of the problem. 



Specimen ivitk Soldered Attachment under Test. — We have suc- 

 ceeded in soldering on the electrodes to one specimen now under test, 

 and are able to preserve the condenser for a more extensive study of 

 its characteristics. Up to the present this study has not added any- 



TABLE VIII. 

 Equations Used in Calciilating Values in Tables VI. and VII. 



thing to the results given above. The new condenser leaks badly in 

 one direction but very little in the opposite direction of charge. We 

 are putting it through an ageing process before submitting it to final 

 measurement. 



Microscopic and Electrical Exploration of the Specimens. 



Illumination and Magnification. — Plate I. contains some micro- 

 graphs of fragments of the crystals. These pictures — which are re- 

 produced with a magnification of 20 diameters — were obtained by 

 reflected light, with the aid of an illuminating objective. The light, 

 which entered the side of the objective, was reflected downward by a 

 prism so that it fell nearly perpendicularly upon the face of the crystal. 

 This vertical illumination from above is most favorable for showing the 

 stratifications in the crystals. Viewed by transmitted light the char- 

 acteristics are hardly discernible. 



Micrograph a, Plate I, shows two of the crystallographic angles of 

 the carborundum crystal. The distance between these two vertices is 

 1.6 mm., and will serve as a convenient standard of reference for the 

 dimensions of the other pictures, which were magnified to the same 

 scale. 



Conducting and Insulating Strata. — Micrograph c shows very clearly 

 the characteristic stratification, which we have found to be the founda- 



VOL. XLVII. — 52 



