Forces of some Metallic Alloys in Contact with Copper. 31 



tained may be employed, because the values of « which were 

 calculated from them are, as Edlund has shown, proportional to 

 those furnished by the readings after 45 minutes. By special 

 experiments, which shall in due time be given, it was ascer- 

 tained that there was this proportionality even when the unsil- 

 vered cylinders were employed. Hence in the present investi- 

 gation, except where otherwise stated, the readings were every- 

 where taken every quarter of an hour. 



As essential parts of the apparatus the double cylinders made 

 of metal sheet and filled with water must be mentioned, the 

 mantles, which protected the copper cylinders against the varia- 

 tions of temperature in the observation-room. Those employed 

 by M. Edlund were made of zinc. During the experiments the 

 oxidating action of the water had covered the inner sides of the 

 mantles with a thick layer of hydrate of zinc, which obstructed 

 the passage of the heat developed in the air-thermometer into 

 the water. Thereby was produced an elevation of temperature 

 in the annular layer of air between a cylinder and its mantle ; 

 and because this rise of temperature was not equally great for 

 both cylinders, the column of liquid in the glass tube was put 

 in the above-mentioned continuous motion towards one side. 

 To remove this a means was tried which is indicated in M. Ed- 

 lund's memoir. New mantles were procured, of the same di- 

 mensions as the old, but of sheet brass and electroplated with 

 silver on the side presented to the water*. These were filled 

 with distilled water. With this arrangement the continuous 

 motion almost entirely disappeared; only towards the end of the 

 investigation did it show itself in a slightly higher degree. The 

 reason for it, however, did not lie in the mantles ; for the dis- 

 placement in question vanished again when an experiment was 

 made with the silvered cylinders. Probably one of the unsilvered 

 cylinders had undergone a change, so that it gave up the heat 

 with greater or less velocity than the other. On account of the 

 continuous displacement, the deflections given in the following 

 are in every case calculated, according to the method before- 

 mentioned, from three deflections observed in succession. 



2. The galvanic current was generated by a pile of from two 

 to four Bun sen's elements ; and in the circuit, besides the wires 

 in the cylinders, a rheostat, a tangent-compass, and a commu- 

 tator were inserted. The alloys, except the German silver, were 

 cast in a mould of gypsum, in cylindrical rods of about 18 cen- 

 tims. length and 2 millims. thickness. These were soldered 

 with tin to copper wires 1 millimetre thick, which had been 

 drawn out of chemically pure, galvanically precipitated copper. 



* The entire apparatus in this improved form is delivered by M. Soren- 

 sen, of Stockholm, at the price of 110 thalers Prussian currency. 



