Prof. H. L. Calleudar on Platinum Thermometry. 191 



These real resultants of imaginary waves are not plane 

 waves. They are forced linear waves sweeping the interface, 

 on which they travel with velocity a~ ] ; and they produce 

 disturbances penetrating to but small distances into the 

 medium to which they belong. Their interpretation in con- 

 nexion with total internal reflexion, both for vibrations in the 

 plane of the rays, and for the simpler case of vibrations 

 perpendicular to this plane (for which there is essentially no 

 condensational wave) constitutes the dynamical theory of 

 FresnePs rhomb for solitary waves. 



XIII. Notes on Platinum Thermometry. By H. L. Cal- 

 LEKDAK, M.A., P.P.S., Quain Professor of Physics, Uni- 

 versity College , London*. 



SINCE the date of the last communication, which I made to 

 this Journal in February 1892, I have been continually 

 engaged in the employment of platinum thermometers in 

 various researches. But although I have exhibited some of 

 my instruments at the Royal Society and elsewhere and have 

 described the results of some of these investigations, I have 

 not hitherto found time to publish in a connected form an 

 account of the construction and application of the instruments 

 themselves, or the results of my experience with regard to the 

 general question of platinum thermometry. As the method 

 has now come into very general use for scientific purposes, it 

 may be of advantage at the present time to collect in an 

 accessible form some account of the progress of the work, to 

 describe the more recent improvements in methods and 

 apparatus, and to discuss the application and limitations of 

 the various formulas which have from time to time been 

 proposed. 



The present paper begins with a brief historical summary, 

 with the object of removing certain common misapprehensions 

 and of rendering the subsequent discussion intelligible. It 

 then proceeds to discuss various formulas and methods of 

 reduction, employing in this connexion a proposed standard 

 notation and nomenclature, which I have found convenient in 

 my own work. I hope in a subsequent paper to describe some 

 of the more recent developments and applications of the 

 platinum thermometer, more particularly those which have 

 occurred to me in the course of my own work, and which have 

 not as yet been published or described elsewhere. 



* Communicated by the Author. 



