552 Dr. A. Matthiessen on the Expansion [Dec. 21, 



I. On the determination of the coefficients of the linear expansion of cer- 

 tain glass rods. 



These rods (1825 millims. long and of 20 millims. diameter) were kindly 

 made for these experiments by Mr. F. Osier. The method used for the 

 determination of their increment in length was that of measuring it with a 

 micrometer-screw, with which a length could be measured with accuracy 

 to 0-001 millim. 



The rod was placed in a long trough, the one end of the rod resting 

 against a fixed glass tube capped with zinc, the other against another glass 

 tube the other end of which rested against the micrometer-screw. Water 

 was allowed to flow through these glass tubes during the time of observa- 

 tion. The trough being filled with water at ordinary temperature and the 

 position of the screw read off, the water was heated to boiling and another 

 reading taken. 



The mean of sixteen observations gave for the linear expansion of these 

 rods 



L,=L (1+0-000007290, 

 and therefore for the cubical expansion 



Y,=V (1+0-000021870- 



II. On the method employed for the determination of the cubical expan- 

 sion of water and mercury. 



This part of the paper contains a full description of the apparatus em- 

 ployed, and the precautions taken. 



The method consists of weighing the substances in water at different 

 temperatures, and from the loss of weight in water deducing its volume. 

 For this deduction, the expansion of water at different temperatures is 

 required. 



III. On the redeterminations of the coefficients of expansion of water. 

 To determine these, pieces of the glass rods (the linear expansion of which 



had to be determined), ground to the shape of a double wedge, were weighed 

 in water of different temperatures. Three pieces of glass were used (making 

 three Series), the weighings being made at temperatures between and 100, 

 the whole number of observations being thirty-two. 



From these it was found that the expansion of water between 4 and 100 

 may conveniently be expressed between 4 and 32 by the formula 

 V,= 1-0-0000025300 (-4) + 0-0000083890 (#4) 2 -0-00000007173(-4) 3 

 and between 32 and 100 by 

 V,=0-999695 + 0-0000054724 2 -0-000000011260* 3 . 



The values calculated from these formulae for the volume occupied by 

 water at different temperatures are given in Table I. from degree to degree 

 together with the differences for each degree. 



