276 proceedings: phil,osophicai. society 



operations— addition, multiplication, inner multiplication, outer multi- 

 plication, and differentiation— may be chosen as indefinables. 

 As postulates for Mathematical Physics, we may choose: 



1. The principle of dimensional homogeneity. 



2. The principle of the relativity of size. (Similitude.) 



3. The principle of the relativity of motion. 



4. Hamilton's principle. (Corollary Conservation of Energy.) 



5. The principle of the constant velocity of light. 



6. The principle of the indivisibility of the electron. 



7. The principle of entropy increase. 



8. The principle that crystals have zero entropy at the absolute zero. 



9. Some principle for quantum action which is not yet known. 

 These postulates furnish the methods of operation for handling the 



greater bulk of the material treated in Mathematical Physics. 



Discussion: The paper was discussed by Messrs. Humphreys, 

 Hawkesworth, Lloyd, Hull, Foote, Bauer, White, Agnew, and 



TUCKERMAN. 



Mr. E. F. Mueller next presented a paper on The standard scale 

 of temperature by C. W. Waidner, E. F. Mueller, and P. D. Foote. 



The standard scale of temperature which it is attempted to realize 

 in practice is the centigrade thermodynamic scale. Owing to the 

 experimental difficulties involved in the use of the gas thermometer, 

 it is necessary to establish a working scale, which should represent the 

 thermodynamic scale as closely as is possible in the light of existing 

 knowledge. It is equally important, however, that the working scale 

 be characterized by a high degree of definiteness and reproducibility. 

 The working scale is defined by means of certain fixed points, such as 

 freezing or boiling points, and by specifying the method of interpolation 

 between the fixed points. In 1914, the three leading national labora- 

 tories, the Physikalish-Technische Reichsanstalt, the National Physical 

 Laboratory and the Bureau of vStandards had practically agreed on the 

 details of a working scale. While the scale was not formally adopted, 

 each laboratory has adopted it independently, there being only minor 

 difi"erences between the three. In the interval — 190 degrees to +450 

 degrees, the fixed points are those defined by the boiling point of oxygen, 

 sublimation point of CO2, freezing and boiling points of water, and the 

 boiling point of sulphur, and the platinum resistance thermometer is 

 used as the interpolation instrument. In the interval 450 degrees to 

 II 00 degrees the platinum — 90 per cent platinum, 10 per cent rhodium 

 thermocouple is used as interpolation instrument, being calibrated at 

 the freezing points of zinc, antimony and copper. A number of fixed 

 points in addition to those given were also agreed upon. 



In the negotiations between the laboratories, no attempt was made to 

 define a scale above iioo degrees. Present practice, however, tends 

 toward using the disappearing filament type of optical pyrometer as an 



