636 PROCEEDIXGS OF THE AMERICAN ACADEMY. 



After the observations of December 10, on the Hall effect, it was 

 found that the plate had been several millimeters too high in the 

 magnetic field during the observations of December 3 and 10, so that 

 the strength of the field to which it had been exposed was some- 

 what uncertain. Proper adjustment was made December 22, and 

 later in the same day the Hall effect was measured again at low tem- 

 perature. The coefficient found December 22 was about 3.3 per cent 

 lower than that of December 3, though the temperature on the later date 

 was only 0.4° lower, which would account for scarcely 0.5 per cent differ- 

 ence. For the value oigTe at the mean low temperature, 12.9°, we have 

 taken the mean, 794 X 10~^ of the values found on December 3 and 

 December 22. For the value of eTe at the high temperature, 84.5°, 

 we have taken the value found December 10 reduced by 1.5 per cent, 

 thus getting 1464 X 10-^ 



For the temperature-coefficient of « T^ in Plate 2, we get 



(1464 - 794) -^ 794 (84.5 - 12.9) := 0.0118.5 



Ettingshausen Effect. — With Plate 1 we undertook to measure this 

 effect by using the east and the west coils of our galvanometer differen- 

 tially, connecting the I^It circuit with the west coil and the C2C4 circuit 

 with the east coil and taking care to have the total resistance of one 

 circuit equal to that of the other. This arrangement we called {h-I*) 

 versus {C^-C^. Lest there might be error from a possible accidental 

 advantage of one coil of the galvanometer over the other in action upon 

 the needle, a series of observations made with this arrangement was 

 always coupled with a {C^-C^ vs. {h-T^ series, in which the C2 T^ 

 circuit was connected with the west coil and the hli circuit with the 

 east coil. 



The theory of this test was that the Hall effects in the two circuits 

 would just neutralize each other, leaving the Ettingshausen effect in 

 the ("2 (-\ circuit to give an account of itself in the net result. This 

 experimental method was not so good as that used in the study of the 



* Dr. Alpheus W. Smith gave in the Physical Review for Jan., 1910, the 

 results of his study of the Hall effect in various metals through a large range 

 of temperature. Taking data from the diagrams of his paper, we find as the 

 temperature-coefficient of the Hall effect 



0.0088 between 22° and 100° in " Kahlbaum iron," 

 0.0140 " 23° " " " electrolytic iron. 



The mean of these values, 0.0114, agrees very well with the values found by 

 us in Plates 1 and 2. 



