6 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Curves A and B given in the above table are plotted in the diagram, 

 which explains itself. 



Min 



2 Min. 

 Figure 1. 



3 Min. 



4 Min. 



The application of these results to a calorimetric experiment is very 

 simple. Obviously, the thermometer will always lag as much behind the 

 temperature of a given bath of changing temperature as it was behind 

 the bath at the time when its own temperature was changing at the same 

 rate as that of the bath. Because the tangent of a curve at any point in- 

 dicates the direction of the curve at that point, the lag is simply found by 

 determining the point at which a line drawn at the required angle just 

 touches the curve. For example, if the bath were cooling 0.020° per 

 minute, the ordinate of the point of contact of the curve with a tangent 

 drawn at the corresponding angle (0.02° per minute) in the diagram will 

 give at once the lag. Thus in the case of the present thermometer, the 

 lag would be 0.017° (Curve A) if the liquid were not stirred, and 0.004° 

 (curve B) if it were stirred, as indicated by the tangents drawn on 

 the diagram. Even in the most favorable case, the correction would 

 probably amount to over 0.001°, and should therefore always receive 

 consideration. 



