284 DR. A. MATTHIESSEN ON THE EXPANSION 



where N is equal to the number of degrees exposed, T the uncorrected temperature of 

 the water, and t the temperature of the thermometer the bulb of which is placed in 

 contact with the stem of the other thermometer halfway between the top of the mer- 

 cury column and the middle of the cork. The number given is the apparent expansion 

 of mercury in glass. 



Having thus described the diiferent parts of the apparatus, I will proceed to state the 

 iaanner of making the determinations. The different parts having been placed together, 

 the trough was filled vdth water by connecting the tap F with the water-tap ; and when fuU 

 the water was still allowed to enter, escaping through a waste-pipe at the top of the 

 other end of the trough. After the water had flowed through the trough for about half 

 an hour, it was turned off at F and connected with d, flowing through B, and thence 

 passing through the rubber tubing from c tof. At /'it enters the tube C, and escapes 

 "at g into a waste-pipe. The temperatures of the thermometers having been read off, 

 and the position of the screw noted when touching the end of the tube C, the eighteen 

 Bunsen burners were lighted, the screw at the same time being turned so as to allow 

 for the expansion of the rod. When the water boiled the temperatures were read off, 

 and the new position of the screw noted on touching the end of C. It was found 

 necessary to continue boiling the water for about a quarter of an hour before constant 

 readings could be obtained. To take the readings again at low temperatures, the 

 water-tap was connected with F, and the water allowed to flow through the trough till 

 that flowing from the waste-pipe had the same temperature as the water from the tap, 

 when the connexion was again made with d. To obtain this temperature, it took from 

 three to four hours. It may here be mentioned that screens were placed between the 

 ends of the trough and the tubes B and C, to prevent their being heated by radiation 

 from the trough whilst making the observations at high temperatures. A thermometer 

 placed near the screw of the measuring-apparatus showed no change of temperature 

 during the time of the experiment, the room in which the experiments were made 

 being a very large one. 



Only such observations were deemed reliable as gave concordant results on heating and 

 cooling the rod, the slightest movement in any part of the apparatus causing large 

 differences in these values. No good results were obtained at first, but after some 

 practice the values found agreed well together. These are given in Table I. 



Nos. 1, 2, & 3 are the observations made with Rod I., with only two springs in the 

 trough. 



Nos. 4 & 5, the observations made with Rod I., the apparatus having been taken to 

 pieces and put together again ; the rod also being turned, and four springs being 

 used. 



Nos. 6 & 7, the observations made with Rod II., with four springs. 



No. 8, the observations made with Rod II., with four springs, rod turned, and appa- 

 ratus readjusted. 



Table II. gives some measurements which prove that the increment in length between 



