180 S. R. Williams — Lavoisier and Laplace's Method. 



Art. XX. — A Modification of Lavoisier and Laplace's 

 Method of Determining the Linear Coefficient of Expan- 

 sion • by S. R,. Williams. 



A General Laboratory Method. 



The first accurate determinations of the Linear Expansion 

 Coefficients of solids were made by Lavoisier and Laplace* in 

 1782. The rods, whose change in length with temperature 

 they investigated, were placed in a water-bath with one end 

 clamped firmly against a rigid wall, while the other end was 

 fastened to a lever which rotated a telescope about a horizon- 

 tal axis. The telescope was directed toward a vertical scale 



Fig. 1. 





r- : 



4 





m~\ 



I 





■-■■-. 







: 







' m '"** 



frlBi 



and from the deflections the changes in length were determined 

 as the temperature of the bath was varied from 0° to 100° C. 



In the following I wish to describe a simple modification of 

 Lavoisier and Laplace's method which overcomes several diffi- 

 culties encountered in that of the original as well as in the 

 numerous devices now used for this experiment. 



Figure 1 shows the apparatus as used in the laboratory, and 

 figure 2 shows it schematically. The steam-jacket, A, encloses 

 the rod, R, whose change in length is to be studied. 



* Lavoisier and Laplace, Bot. Traite de Physique, vol. i, p. 151. 



