10 Ml;. .). 11. CIMNDLKY OX AX KXI'KIMMKXTAI. IXVKSTIGATION OF 



SECTION VI. On the Methodx of Detcrminiiuj the Pr<'**<tres and Temperatures. 



Into the reservoir RR a tube of brass aa, closed at the bottom, penetrates, as 

 shown in fig. 2. This tube contains oil, and in it a thermometer is placed ; the length 

 of this thermometer immersed in oil being a matter of importance, it was sought to 

 keep the amount of oil in the tube as constant as possible during the experiments. 



The pressure of the steam before entering the orifice was observed on a Bourdon 

 pressure gauge, the siphon from which enters the steam channel at S, between the 

 reservoir and the orifice. 



The pressure of the wiredrawn steam was observed, during the experiments with 

 steam from the Lancashire boiler, by a mercury pressure gauge, and afterwards by a 

 second Bourdon pressure gauge, the siphon from which passed through the jacket 

 surrounding the channel, and entered the channel at S,, fig. 3. 



The temperature of the wiredrawn steam was determined by inserting a thermo- 

 junctiou of iron and copper into the steam channel, as at t. 2 t.,, fig. 3, the wires passed 

 out of the channel through two small glands in a brass plug, the joints being made 

 with asbestos, which also formed the insulator for the wires. A second similar 

 thermo-junctiou in circuit with the first is placed in an oil bath, the temperature in 

 which could be adjusted to any required degree, the oil being stirred by two screw 

 blades, worked by a small water motor. In this bath a thermometer was fixed, 

 and the equality of temperature between the junction in the oil and the junction in 

 the steam was shown by a galvanometer with mirror and scale. The ends of the 

 copper wires from the two junctions dipped into two small mercury cups, and the 

 ends of two copper wires from the galvanometer were dipped into these cups, 

 completing the circuit. If any difference of temperature existed between the 

 junctions, the galvanometer needle would be deflected, and by diminishing these 

 deflections by altering the temperature of the oil bath, the final equality of tempera- 

 tures between the thermo-junctions in the steam and oil was determined. 



The difference of temperature between the steam in the jacket and the wiredrawn 

 steam was observed by having a thermo-j unction similar to that in the wiredrawn 

 steam placed in the steam jacket at t 3 , fig. 4 ; a second similar junction was placed in 

 the oil bath mentioned above. 



These two junctions could now be brought into circuit with the galvanometer in 

 a precisely similar manner to the other pair of junctions in the oil bath and the wire- 

 drawn steam, as described already. When the oil bath temperature has been 

 adjusted to equality with that of the wiredrawn steam, the galvanometer was imme- 

 diately brought into circuit with the junctions in the oil and the steam jacket ; any 

 deflection of the galvanometer needle would now be proportional to the difference of 

 temperature between the oil and the steam in the jacket, and therefore to the 

 difference in the temperatures of the wiredrawn steam and the steam in the jacket. 



The use of thermo-electric junctions to determine the temperature of the wire- 



