258 gray: linear expansivity 



Jaquerod and Perrot 6 sought to avoid them by the use of fused 

 silica, whose expansivity is small. Day, Clement, and Sosman 7 

 conducted elaborate secondary investigations to determine the 

 linear expansivity of rods, the composition of which was made as 

 nearly as possible the same as that of the bulb, though the physical 

 treatment of the two must of necessity have been decidedly dif- 

 ferent. Apparently, however, in no case have changes in the 

 dimensions of the bulb itself been measured simultaneously with 

 the measurements of pressure necessary to determine the tem- 

 perature. 



The possibility is here suggested of accomplishing this by 

 the method described in the first section of this paper. The 

 wires for transferring the displacements could be applied to the 

 ends of a thermometer bulb, the capillary of which is placed a 

 little to one side of the axis for the purpose of leaving the adja- 

 cent end unobstructed. These same measurements yield the 

 expansivity of the material of the bulb, using the bulb itself as 

 an integrating thermometer. The openings necessary for the 

 wires can be arranged so as not to disturb the temperature dis- 

 tribution within, and can be used for admitting a gas to equalize 

 the pressure on both sides of the bulb walls. 



It is obvious that the method, which determines total linear 

 change, whether arising from thermal expansion or other influ- 

 ences, could be used for following alterations of the bulb in other 

 directions. 



It is also suggested that the methods of temperature control 

 discussed above might possibly be advantageously employed in 

 this connection. 



6 A. Jaquerod and F. L. Perrot, Archives des Sciences Phys. et Nat. 20: 35. 

 1905. 



7 A. L. Day and J. K. Clement, Am. Jour. Science 26: 405. 1908. A. L. Day 

 and R. B. Sosman, Am. Jour. Science 29: 93. 1910. 



