278 PROCEEDINGS OF THE AMERICAN ACADEMY. 



There are thirteen of these fine wire junctions on each side of the 

 disk, those on the upper side being arranged and nnmbered as shown 

 by Figure 4. On the under side are corresponding jnnctions, 1' just 

 beneath 1, 2' just beneath 2, 3' just beneath 3, etc. The method of 

 combining these junctions and the method of estimating the mean dif- 

 ference of temperature between the two copper-steel surfaces, by 

 means of the thermo-electric currents sent through these junctions to 

 a galvanometer, will be described later. 



The parts ^1 andj^, in Figure 1, are copper- German-silver junctions. 

 The German-silver wire g s, about 0.015 cm. in diameter, is contin- 

 uous from one junction to the other. At each junction the German- 

 silver wire is joined to a copper wire, about 0.010 cm. in diameter. 

 From each junction the two wires, separated by a stri[) of plastic non- 

 conducting material ("Jeukin's packing "), y, are led into and along 

 a plug, p, consisting of two half-cylinders of hard rubber held firmly 

 together by clamps k and k. Within this plug the fine copper wire is 

 attached in a soldered joint to another copper wire, W, about 0.06 cm. 

 in diameter, which leads away toward a galvanometer. The loop of 

 wire exposed to the water near each junction is coated with varnish 

 to prevent disturbance due to chemical action. Shellac, baked on, 

 seems best for this purpose. The water, as the arrows indicate, 

 passes j\ on entering, and jz on leaving, the upper chamber of the 

 apparatus. The thermo-electric current from these junctions shows, 

 when interpreted, the difference of temperature of the incoming and 

 outgoing streams. 



The amount of water flowing through the apparatus per second, 

 about 24 grams, was measured by noting the time required to fill a 

 flask of known capacity, F, in Figure 5. This time was about 75 sec- 

 onds, and it was observed at stated intervals by means of an ordinary 

 watch. The devices used for making this flow nearly constant, for an 

 hour or more at a time, will be described later. 



JJ, in Figure 1, is a double-walled copper jacket, supported by 

 means of lugs, /, I, upon the ring bb, a. thick piece of rubber under the 

 end of each lug preventing metallic contact with b. The water, after 

 passing the junction yg on its way out, entered this jacket near the 

 bottom, flowed around and upward and escaped by the orifice into a 

 descending tube, the lower end of which was kept at any desired level, 

 usually lower than any point shown in the figure. Thermometer 7\, 

 passed by the stream on its way to^i, and T2, in the jacket near the 

 exit, gave a rough indication of the change of temperature suffered by 

 the water between these two points. It was usually about 1° C. when 



