758 REPORT— 1894. 



instead of 18,000 — and although in every heat there are three processes, the whole 

 follow so smoothly that the progression of the hand is practically continuous. 



5. On a Direct Reading Forin of Platinum Thermometer. 

 By G. M. Clark, B.A. 



The author described the pyrometer of Callendar and Griffiths. In this instru- 

 ment the leads to the platinum coil are so arranged that only a single observation 

 is necessary to determine its resistance. Further, by constructing the galvano- 

 meter so that its deflections are independent of the E.M.F. of the battery, the 

 same increase of resistance of the coil will always give the same deflection on the 

 pcale. A wide range of temperature as well as an open scale is secured by the 

 galvanometer being brought back to zero every hundred degrees. It is also pomted 

 out that the ' fixed points' of these thermometers are not liable to variation. 



As reliable experiments with the air thermometer above 700° C. have not yet 

 been carried out, the author suggested the adoption of a platinum thermometer 

 with fixed coefficients as a standard. 



TUESBAY, AUGUST U. 

 The following Export and Papers were read : — 

 1. The Report of the Committee on Dryness of Steam. — See Reports, p. 392. 



2. On the Temperature Entropy Diagrams. 

 By H. F. W. BuRSTALL, M.A., A.M.Inst.C.E. 



The treatment adopted in this paper has been to consider the temperature 

 entropy diagrams, from the engineer's point of view, and as far as possible graphical 

 methods are alone employed. 



The reason of the great value of the diagrams lies in the fact that an area 

 represents the heat required to effect the change denoted by the contour of the area ; 

 and when the actual expansion of the steam is plotted on the heat diagram it is 

 easy to see by inspection where the losses of heat have occurred. 



The ordinates of the curves are the absolute temperature and the entropy or 

 heat weight. 



The curves denoting the heat required to form a given mixture of steam and 

 water can be drawn once for all ; after that very simple arithmetic is all that is 

 required to trace the expansion curve for any engine on the heat diagram. 



The changes in the pressure and dryness of steam confined in a constant volume 

 are shown by means of a model in space, in which the vertical distances represent 

 the volume of steam, and the horizontal plane a temperature entropy diagram. 

 On cutting the surface formed by a plane parallel to the horizontal plane we have 

 a curve which gives the constant volume curves, and the construction follows at 

 once from the model. 



The paper was illustrated b}' diagrams from several types of steam engines, both 

 compound and triple expansion, and the diagram for a gas engine was also shown. 



3. On the Hunting of Governed Engines.^ 

 By James Swinburne, M.Inst.C.E. 



Governors are generally considered as complete mechanisms without reference 

 to the engines governed. Hunting, however, depends, not only on the governor, 



' Published in full in Engineering, August 17, 1894. 



