16 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the cooling curve be correct as first taken. The usual method requires 

 the taking of the heating curve, i. e. the remelting of the alloy, in 

 order that we may apply an incorrect formula to give us the tempera- 

 ture of such transformations as are registered on these insensitive 

 curves. This method is cumbersome and, unless the rate of cooling is 

 very slow, is inaccurate. And when we have taken the heating and 

 cooling curves and found the so-called temperature of transformation, 

 it is a question as to what alloy the data belongs. 



The tube-form of couple makes it possible to take an accurate cool- 

 ing curve for slow rates of cooling, and even such rates as are employed 



Fig. 4. 



in tempering can be taken with a fair degree of accuracy. Thus the 

 second main difficulty in the study of alloys is largely removed. 



Description of the Apparatus. 



The recording device. — Figures 3 and 4 represent a top and side 

 view, respectively, of the recording part of the apparatus. A simplified 

 form of Einthoven galvanometer G, in circuit with a thermo-couple, 

 gives the difference in temperature between the hot and cold junction. 

 An ordinary projecting lantern J throws a beam of light through S2 

 and illuminates the filament /of the galvanometer. By means of the 

 lenses /, the light from the filament is focussed on the drum r of a 

 chronograph. The screen S carries a narrow slit parallel to the axis 

 of the drum, and thus allows only a spot of light to reach the sensitive 

 film F which is fastened about the drum. A variation in the tempera- 

 ture of the hot junction causes the spot of light to move along the 

 drum in a direction parallel to its axis. If such a movement takes 

 place while the drum rotates, a curve is photographed on the film, the 

 coordinates of which are temperature and time. 



