HALL. — TIIEEMAL AND ELECTRICAL EFFECTS IN SOFT IRON. G03 



any junction should be very small in the neighborhood of that junction. 

 All the wires, after leaving the packing surrounding the bars, ran nearly 

 straight upward to a wooden platform about 30 cm. above the outer 

 guard-ring. Here all the copper wires were connected with larger 

 copper wires leading off toward the du Bois and Rubens Panzer- 

 galvanometer with which all the thermo-electric currents were meas- 

 ured, while all the German-silver wires were continued to the Crafts 

 boilers, about 1 meter distant. 



To obstruct the lateral flow of heat from the main bars outward, the 

 outer guard-ring was covered, except at the top, where the wires came 

 through, by a wrapping of magnesia and asbestos about 2.5 cm. thick, 

 and the space within was stuffed rather loosely with wisps or wads of 

 asbestos fibre. Concerning this packing something will be said later. 



The space between the square pots was closed on both sides by thick 

 asbestos board, between which and the packing outside the outer guard- 

 ring there was at mid-level an interval about 2 cm. wide. 



The space beneath the packed bars was walled in on all four sides by 

 similar asbestos board, which was intended to prevent, to a great degree, 

 circulation of air, and especially of hot gases from the large Bunsen- 

 burner flames used beneath the pots, from passing up past the bars. 

 The space above the bars, up to the wooden platform already mentioned, 

 was boxed in in the same way, though there were, before April 13, 

 two gaps near the top of this enclosure, through which escape of air 

 from the interior was facilitated, it being at first considered unsafe to 

 close in completely the space under the wooden platform. 



Study of the Lateral Flow. 



The first observations of this kind were made January 26-27, 1906. 

 Both pots contained water boiling at atmospheric pressure, and the 

 outer junctions of all the thermo-electric couples a, h, c, d, and e 

 connected with the main bars and the guard-ring bars were placed 

 in two of the Crafts boilers containing water boiling at atmospheric 

 pressure. 



The time at which boiling began is not recorded in this case. 

 Observations to test the approach of the bars to a constant condition 

 of temperature began about G p. m., January 26, and were continued 

 about two hours, the indications being that a fairly stable condition 

 had been attained by 8 p. m. The boiling was continued, however, 

 till past midnight before any of the thermo-electric observations finally 

 used were made. 



The final operations were substantially as follows, though not made 

 in the precise order here given : — 



