504 Mr. A. W. Warrington on 



degree. The doors were then closed and another experiment 

 made. 



Any mist which might form on the inside surface of the 

 inner glass door was dissipated by cautiously warming the 

 outside surface with a spirit-lamp. 



Experiments 1 to 23 inclusive were made with a falling 

 thermometer. The fall of the thermometer appeared in all 

 cases to be perfectly uniform. 



Experiment 39 is given in detail in Appendix E. 



Determination of the Coefficient of Expansion of Normal 

 Jena Glass. 



The hydrometer designed for liquids was made in July 1897 

 of normal Jena glass, and is weighted with mercury. It is 

 202 mm. long and 41*5 mm. diameter in its widest part. It 

 is depicted in fig. 1. 



Its weight, as determined from the data given in Table I., is 

 160-21506 + 0-000077 grammes. 



If W be the weight in vacuo of the hydrometer itself and w 

 the weight in vacuo of the platinum which must be added just 

 to submerge the instrument in water the specific gravity of 

 which is p, then 



, r W + iv „ W + io—pv 



P P 



in which V = the volume of the hydrometer itself, 



and v —the volume of the added platinum. 



The values for w were determined with such care that they 

 were probably correct to 0'02 mg. 



Six determinations (see Table II.) gave 2T450 + 0-002 as 

 the mean specific gravity of the platinum used. Owing to 

 the high specific gravity of platinum and the very small 

 quantity of it used, v can be calculated with sufficient accuracy 

 to admit of the determination of V in the above equation. 



The volume of the hydrometer at 0° when the first expe- 

 riment was made was 161*92982 cub. centim. 



Experiments made at approximately the same temperature, 

 but on different days, proved not only that the volume of the 

 hydrometer was continually contracting, but also furnished 

 data for a quantitative estimation of the rate of contraction. 



The mean expansion of the hydrometer between 0° and 40° 

 for one degree is about 0"0039 c. c. Hence if the volume of 

 the hydrometer at temperature t be Y t , then its volume at 

 temperature t 1} when t = ti + 0°"2, on the same day, is given 



