AUGUST 19, 1921 PROCEEDINGS : PHILOSOPHICAL SOCIETY 349 



value. The passing of the circuit from the non-oscillating to the oscillating 

 state results in a rise in plate current sufficient to operate the telegraph relay. 

 The operation of the relay results successively in a pen excursion and in the 

 killing of the local oscillations. The circuit is thus restored to the receptive 

 state and the pen to the datum line. 



A very small change in grid potential is sufficient to start oscillations if the 

 grid potential is initially adjusted to a value near to and just below the 

 critical potential. This potential rise may be provided by a radio signal 

 received on an antenna suitably related to the regenerative circuit. 



The circuits are so located that during the reception of radio signals the 

 breaks of a local break-circuit chronometer may be recorded simultaneously by 

 means of the same pen. This obviates lags which would be encountered if 

 independent pens were used. 



850th meeting 



The 850th meeting of the Philosophical Society was held in the Auditorium 

 of the Cosmos Club on April 9, 1921. It was called to order by President 

 Paris with 31 persons present. 



The first paper, on Mollier diagrams, by E. F. MuELLER and C. H. Myers, 

 was presented by Mr. Myers and was illustrated. 



In 1904 Mollier published an article^ in which he described the properties 

 of heat content and its uses in refrigeration problems. This article is illus- 

 trated with (1) a heat content-entropy diagram with rectangular coordinates 

 for steam, (2) a heat content-entropy diagram with oblique coordinates 

 for CO2, and (3) a heat content-pressure diagram for CO2. 



In the present paper the properties and uses of heat content were discussed, 

 and illustrations of six diagrams shown in which the ordinates were heat 

 content and the abscissas were entropy (rectangular coordinates), entropy 

 (oblique coordinates), volume, log volume, log pressure, and a scale of pressure 

 corresponding to a uniform scale of saturation temperature, respectively. 



The choice of coordinates is a matter determined by conditions. Where 

 the whole range from saturated liquid to a considerable superheat in the 

 vapor is required the heat content-entropy diagram is poor even with the 

 oblique coordinates since it covers only a small portion of the paper and the 

 lines cross at sharp angles. The use of volume as abscissa is very little if 

 any improvement, although the use of log volume is much better. The 

 diagrams in which a function of the presstu-e serves as abscissa are very read- 

 able, although the pressure corresponding to a uniform temperature scale 

 is probably the best when the diagram does not extend above the critical. 



Some function of the heat content might be used for the ordinate in order 

 to magnify the scale in parts desired to be especially accurate. The use of 

 uneven coordinates should cause very little trouble if sufficient lines are 

 entered in the diagram so that linear interpolation may be used. 



The second paper, on The heating of substances by expansion, was presented 

 by Mr. ly. H. Adams, and was illustrated. 



The pressure to which a fluid is exposed may be released by three princi- 

 pal methods : 



(1) Isentropic expansion, i.e., at constant entropy. 



(2) Isenergic or explosive expansion, i. e., at constant energy. 



* Zeitschr. Ver. Deutscher Ingen'.eure. 



