320 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and a range of voltage between 1.5 and 6 volts (alternating) did not 

 differ from the corresponding values at the beginning of the series by 

 an amount exceeding the limit of accuracy of the experiment, which 

 was about ^ of 1 per cent. 



This experiment shows that if there is any kind of electrolytic action, 

 it must be of such a character as not to change the nature of the 

 electrodes or of the crystal. 



On the Question of a Possible Thermoelectric Origin of the Phenome- 

 non. — It is apparent that the disposition of the carborundum for the 

 best rectification is exactly the most favorable disposition for the devel- 

 opment of a thermoelectric voltage at the high resistance contact. This 

 voltage, being always in one direction, by superposition on an alter- 

 nating current through the crystal, might give rise to a unilateral cycle 

 through the crystal. In Part I, several experiments are described which 

 present evidence adverse to this explanation, and the opinion is ex- 

 pressed that " heat is practically a negligible factor in the process." 



However, since it is very important to exclude the possibility of 

 bringing the experiments into consistent relation with thermoelectricity 

 before admitting that we are dealing with a new phenomenon, the 

 question of the applicability of the thermoelectric explanation is taken 

 up anew in the present account. 



Extension of the Experiments to Other Crystals. — Prior to the publi- 

 cation of Part I, the writer had found a number of other crystals show- 

 ing the rectifying property similar to carborundum. These have now 

 been under investigation for a period of more than a year, and though 

 the work is by no means completed, it is thought that an account of 

 the experiments as far as they have gone may be of interest. The 

 present account deals with the rectifying action of Anatase, Brookite, 

 and Molybdenite in contact with a metallic electrode. 



Anatase and Brookite. 



Anatase. — Anatase, an octahedral crystal of oxide of titanium 

 with the chemical formula Ti0 2 , was found to rectify quite markedly 

 when placed in a clamp, under a contact pressure of 1 to 3 kilograms. 

 Current-voltage curves 5 of anatase, with a diagram of the disposition 

 of the crystal in the experiment, are given in Figure 1. The upper curve 

 was obtained when the current was through the crystal in one direction, 



5 The current-voltage curves were drawn in Part I with positive co-ordinates 

 when the current was in one direction and negative co-ordinates when the current 

 was in the opposite direction. In order to economize space in the present account, 

 both the positive and negative currents are drawn in the same co-ordinate quadrant. 

 This has the advantage of permitting an easier comparison. 



