236 



DE. A. MATTHIESSEN ON THE EXPANSION 



or the formula for the correction of the linear expansion of the glass rods will be 



and for the cubical expansion, 



L,=Lo(l+0-000007290, 

 V,=V„(l+0-00002187#). 



In carrying out the foregoing experiments an interesting observation was made ; when 

 the glass rod was heated in the morning for the first determination, the value deduced 

 for the expansion of the rod was greater than those obtained afterwards on the same 

 day — a result Avhich proves that the rod, on being heated, only resumes its normal length 

 after a certain time, and that this gradual change in length is perceptible after twelve 

 to fifteen hours. Table III. gives a few examples of this fact. 



Table III. 



From the above the mean expansion of the rod on first heating between 0° and 100° is 



1-370. 

 The mean of the experiments given in Table I. is 



1-331, 

 making a difference of about 3 per cent, on the expansion*. 



II. On the Method employed for the Determination of the Cubical Expamion of Water 



and Mercury. 



Fig. 5 shows the arrangement of the apparatus used for the determinations. 



Through a small hole in the bottom of the balance and shelf a platinum wire hung 

 from the small pan above. The diameter of the wire is about 0-5 millim. To this 

 wire, by means of a hook, the metal was suspended by a finer wire (0-04 millim. 

 diameter) in the water contained in the box below. The size of the box, measured 

 inside, was 200 millims. cube. It was made of zinc, double sided, and encased in wood. 

 The covers were cut in two to allow them to be put on or taken off" without disturbing 

 the fine wire. Through these, holes were made (fig. 6), a, a for the stirrer, b for the 

 draft pipe, c for the fine wire, and d for the thermometer. The stirrer was a square 

 piece of sheet zinc, soldered to the end of the copper wires R, R, with a hole cut in 



* The rods must have been well annealed, for they stood sudden changes of temperature remarkably well, 

 as shown by the process employed for cooling the water in the trough. 



