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



apparatus this block, against which one end of the rod was 

 placed, was about two inches long, and its expansion from the 

 heat of the rod was quite appreciable. H is an opening in the 

 side of the tube with a cork through which the thermometer, 

 T, is thrust. The base, B, was made from a plank 2x10x24 

 inches, and the back support, Y, was 2x8X31 inches. This 

 stand was made heavy in order that any heating effects from 

 the steam-jacket would not warp or distort it during the experi- 

 ment. In figure 3 is shown the usual support for the steam- 



Fig. 3. 

 . 1 1 /* 



^^gagaazaaz^g^agzzazzzazzzzzzasaa^mp 



jacket, in a horizontal position, which is either of thin boards 

 or a metal bar. A slight pressure at C will change the read- 

 ings altogether, or if the upper side of the base, whether wood 

 or metal, is at a different temperature from the lower the same 

 results will occur. The optical lever for measuring changes in 

 length has been adhered to because it admits of great accuracy 

 and yet is simple. 



The method of focusing the cross wires of two microscopes 

 on the ends of the bar and then by means of micrometer eye- 

 pieces measuring the changes in length is used by the Inter- 

 national Bureau of Weights and Measures, and is very accurate, 

 but for high school laboratories it is too elaborate, and for the 

 average college is rather expensive. 'None of the common 

 methods, as the electric contact, the vernier micrometer and 

 the wooden lever, are as precise as the two mentioned above. 



The vertical position of the steam-jacket and rod makes the 

 use of the optical lever a convenient one, since the back, V, 

 can be made the same height as the rod, and with the mirror, 

 M, on a tripod bridging across from Y to R, the telescope and 

 scale, S, can be put in a convenient position for observations. 



I and O are the openings for the passage of steam through 

 the steam-jacket. In the general laboratory we have taken the 

 length of the bar at room temperature and then again at the 

 temperature of steam, but the apparatus may be very easily 

 adapted to the circulation of water in the steam-jacket and so 

 the lengths for intermediate temperatures may be obtained. 



This apparatus has been in use for two years in the general 

 laboratory, and I have found that the students have reported 

 very concordant results. Its simplicity makes its construction 

 possible with a very limited supply of tools and means. 



Physics Laboratory, Oberlin College, May 12, 1909. 



