

888 Prof. A. W. Porter on the Inversion-Points for 



the rise and fall of sensitiveness to oscillations as the applied 

 E.M.F. is increased. Curves (3) show that if W represents 

 the power in watts delivered to the coherer, and iv the power 

 passed to the telephone circuit, then w = m(W — a) where m 

 and a have values settled by the magnitude of the current 

 through the detector. The quantity m for a good low 

 resistance iron-mercury coherer has been found to be as 

 high as 0-06 ; while a is usually near 1*0 x 10~ 8 watt. These 

 curves show that these coherers are not " voltage-operated " 

 detectors but *' integrating " detectors. 



The author puts forward the hypothesis that the properties 

 of an oxide coherer may arise solely from the temperature 

 variations caused in the minute mass of oxide at the contact 

 by the electrical oscillations and by the applied E.M.F. He 

 examines the hypothesis mathematically, and shows that 

 most of the phenomena recorded in the curves (1), (2), '3) 

 above, can in this way be accounted for as perfectly as the 

 present state of the measurements permits. 



XCII. On the Inversion-Points for a Fluid passing through 

 a Porous Plug and their use in Testing proposed Equations 

 of State. Part II. An Examination of Experimental Data. 

 By Alfred W. Porter, B.Sc, Fellow of, and Assistant 

 Professor of Physics in, University of London, University 

 College *. 



IN a former paper (which will be referred to as Part I.) 

 published in this Journal (April 1906, p. 554) I showed 

 that the usual equations by which the behaviour of real gases 

 is represented indicate that the inversion temperature for the 

 Joule- Kelvin effect must depend upon the pressure, as had 

 previously been found by Witkowski ; and that moreover 

 (as had not been before observed) there must be two 

 inversion-temperatures for each value of the pressure. Of 

 course only such equations were dealt with as indicate the 

 existence of critical phenomena; it would be a very retrograde 

 step at the present day to take others into consideration. In 

 the present paper I gather together as much evidence as I 

 can as to how experimental data support these conclusions. 

 This I have found can be exhibited easily in a form which 

 appeals at once to the eye, and enables one at sight to discri- 

 minate between proposed equations of state. 



* Communicated bv the Author. 



