II ILL/AM .S7/-:.l//:.\-.V, 



369 



investigations by M. (\. \\Yrtlicim, '* winch show a dimiiiu- 

 (ii!i of elasticity with risu of temperature in all metals t- 

 i:.m. This latter metal attains its maximum elasticity (according 

 to this author) at 100 C. ; but annealed cast steel agrees with 

 <:oM ;iinl silver and other metals in showing a diminution of 

 elasticity with rise of temperature. The results given in the 

 table | >r. 'pared by M. "Wcrtheim show a coefficient of diminution 

 '.sticity for cast steel of '000387G8 per degree Centigrade, the 

 modulus of elasticity at C. being lOiiGl, and at 80 C. 1!)01 I. 

 re the bathometer was set up, I had experiments made on the 

 variation of the elasticity of its spiral steel springs in the range of 

 ordinary temperature, which proved this important result, that 

 the elastic force of well-tempered steel springs diminishes with 

 increase of temperature, within the limits of ordinary temperature, 

 in an arithmetical ratio. The coefficient which I obtained from 

 these experiments was '000258 of diminution of elasticity per 

 degree Centigrade rise of temperature ; and the small difference 

 between this and the coefficient deduced from Wertheim's table 

 will be due most likely to a difference of temper in the steel. 



In the bathometer the linear expansion of the springs is 

 compensated by the linear expansion of the tube to which they 

 are attached ; and we have therefore only to deal with the 

 variation of elastic force which has to be compensated for, in 

 order to make the indications of the instrument independent of 

 temperature. 



COMPENSATION FOE TEMPERATURE-EFFECTS. The means of 

 such compensation is provided in the mercury column. If this 

 column were to consist of a plain cylindrical vessel, not subject to 

 change in diameter by temperature, it is evident that its pressure 

 upon the diaphragm would be the same whatever the temperature 

 of the mercury might be; for with increase of temperature the 

 height of the column would increase, and the density of the 

 mercury decrease in precisely the same degree : such a column 

 might be called one of uniform potential, and would not afford the 

 means of compensation here desired. If, on the other hand, the 

 column were made to consist of two shallow cups ab top and 



* Annalcs de Chimie et de Physique, s6r. 3, 1845, xv. 119. "Sur 1'influence 

 des lui'-M^ tciniMTutures sur I'cla.sticit6 des melaux." 



VOL. II. B B 



