PHILOSOPHICAL TRANSACTIONS. 



I. On the Absolute Expansion of Mercury. 



/it/ HUGH L. CALLENDAR, M.A., LL.D., F./'.S., I'rofessor of Physics at the Imperial 



College <j/',SV/o/<v and Technology, S. JT., and HEKBEKT Moss, B.Sc., A.R.C.8., 



Demonstrator of Physics at the Imperial College of Science and 



Technology, London, S. IT. 



Received November 19, 1910, Read January 12, 1911. 



CONTENTS. 



Page 



1. Introduction 1 



2. General description of the apparatus and method 3 



3. Theory and notation 7 



4. Method of filling the apparatus 10 



6. Method of taking observations 11 



6. Method of reducing the observations 13 



7. Summary of observations 15 



Series I. 20 C. to 187 C 16 



Series II. 187 C. to 300 C 19 



Confirmatory series 20 



Series III. - 10 C. to 100 C 21 



8. Empirical formulae for the expansion of mercury 22 



9. Order of accuracy of the results 24 



10. Comparison with previous results 25 



11. Corrected value of the boiling-point of sulphur 28 



12. Explanation of the tables of expansion 29 



1. Introduction. 



THE determination of the expansion of mercury by the absolute or hydrostatic 

 method of balancing two vertical columns maintained at different temperatures does 

 not appear to have been seriously attempted since the time of REGNATJLT (' Me"m. de 

 1'Acad. Roy. des Sci. de I'lnstitut de France,' tome L, Paris, 1847). His results, 

 though doubtless as perfect as the methods and apparatus available in his time would 

 permit, left a much greater margin of uncertainty than is admissible at the present 

 time in many cases to which they have been applied. The order of uncertainty may 

 be illustrated by comparing the value of the fundamental coefficient of expansion (the 

 VOL. cvxr. A 471. B 7.3.11 



