202 harper: thermo metric lag 



forces acting at its boundaries and conduct real energy with a 

 finite velocity and yet itself have no inertia or rigidity in any 

 mechanical sense. 



Two of the many possible explanations are suggested. (1) the 

 properties of the ether may be mechanical after all but in four 

 dimensions. If this be the case it is for the mathematical physi- 

 cist to work out the solution of the problems of gravitation, induc- 

 tion and radiation ; it would be useless for the experimental physi- 

 cist working in three dimensions to seek a solution. Or (2) the 

 properties of the ether may be non-mechanical of unknown nature. 

 In this case, it is for the experimentalist to find out the nature of 

 electricity and ponderomotive electrical effects. The four dimen- 

 sional mathematical method appears to be the only one capable 

 of attacking the gravitational field; yet we feel instinctively that 

 the final solution ?nust be physical and three dimensional. 



PHYSICS. — Thermometric lag. D. R. Harper 3rd. Commu- 

 nicated by C. W. Waidner. To appear in the Bulletin of the 

 Bureau of Standards. 



The transfer of heat from any medium to a mercurial ther- 

 mometer of the common " chemical" type may be expressed with 

 a high degree of accuracy by the relation 



fK<-* (1) 



where 



6 = temperature of thermometer (average) at time t 

 u = temperature of medium at same instant 

 X = a " constant" with respect to 6, u, and t. 

 X is not an absolute constant of a given thermometer but depends 

 upon the medium in which it is immersed and the rate at which 

 the meduim is stirred. By equation (1) it is seen that X has the 

 dimensions of time, and it may be interpreted as a definite number 

 of seconds: 



1 . If a thermometer has been immersed for a long time in a 

 bath whose temperature is rising at a uniform rate, X is the number 

 of seconds between the time when the bath attains any given 



