806 PROCEEDINGS OF THE AMERICAN ACADEMY. 



upon one of the ends may break altogether the electric circuit of which 

 the column of bars should form a part. In later work it seemed better 

 to rub the ends with fine emery paper, and then wipe them upon smooth 

 hard-finished paper to remove adhering particles of dust. 



Bars 1, 3, 5, 7, 9, 11, 14, 17, 19, and 23, the numbers indicating their 

 order from one end toward the other of the slice from which they had 

 been cut, were placed in the order just given, end to end in the appar- 

 atus shown by Figure 5. The resistance of the column, which in the 

 case of soft iron bars had been about 2 ohms under a pressure of 1.8 

 kgm., was now found to be surprisingly large. It diminished with in- 

 crease of pressure, but even with a pressure of 3 kgm. was at first, June 

 30, about 16.5 ohms. Under a nearly continuous application of this 

 pressure it gradually grew less, until, on July 2, it was about 5 ohms, 

 after which it changed but little, although it appeared to be somewhat 

 greater on July 4. 



With this set of bars, and with the method already described, the follow- 

 ing results were obtained : — 



Date. P'? °^ "^^^P- Mean Temp. E. m. f. in Volts per Degree, 



between Lads. "^ r o 



June 30, 1898, 9°.84 29°.3 ) .00000549 1 ......,, 



July 4, " 10°.21 30Mr--' .00000549 P^^^^^^*^ 



" « " 11°.97 45°. 2 .00000593 



" 2, " 13°.40 C3°.2) •^00^0^491 



" 4, « 15M3 63°.0i^^-^ .00000043 r^^^^^^^*^ 



On November 4, 1898, observations were made in the same way with 

 ten cast iron bars taken from the same set as those used in June and 

 July ; whether the same bars or not, could not be told. The result was : 



Date. Diff. of Temp. Mean Temp. E. m. f. per Degree. 



Nov. 4 10°.24 29°.7 .00000550 



It should be remembered that the end to end method of experimenta- 

 tion with short bars of cast iron was adopted because of a doubt as to 

 the availability of the thermo-electric test made by a different method on 

 a 10 cm. bar cut crosswise from the cast iron slab. This earlier method 

 had given : — 



Mean Temp. E. m. f. per Degree. 



14° .00000507 



18°.6 .00000518 



40°.6 .00000576 



63°.3 .00000647 



