178 REPORTS ON THE STATE OF SCIENCE.—1914. 
report of the Committee, and using in his calculations the values of 
the internal energy defined by the curve in fig. 6 of that report. 
In Note 84 Professor Coker describes the method of measuring 
the cyclical temperature in a gas-engine cylinder used by him at the 
Technical College, Finsbury, and gives the results of some recent 
experiments. Curves are included showing the temperature of the 
explosive charge, together with tables of the actual temperatures at 
various points in the cycle. A full description of the thermo-couple 
used in these experiments is given in the Note. 
In connexion with Note 35 Professor Watson showed a series of 
photographs of the spectrum of the light given by the burning charge 
in the cylinder of a petrol engine. The results show that the gases 
in the cylinder continue to emit light giving a line spectrum for a 
considerable time after the chemical changes are generally assumed to 
have been completed. 
Before proceeding to consider the work carried out during the 
current session it has been thought advisable to give a brief summary 
of the previous reports of the Committee. a. 
Summary of Previous Reports. 
The first report is- devoted mainly to the subject of the specific 
heats of gases at high temperatures. The constant-pressure experi- 
ments of Wiedemann, Regnault, Holborn, and Henning are analysed 
and discussed, and a curve is given showing the energy of CO,, steam, 
and air in terms of the temperature Centigrade. The experiments of 
Dr. Dugald Clerk are described, and the results obtained compared 
with the constant-pressure experiments mentioned above. ‘The closed 
vessel experiments of Mallard, Le Chatelier, and Langen are analysed 
and the results plotted and discussed. 
The report ends with the discussion of thermal equilibrium, chemical 
equilibrium, the motion of a gas, and the measurement of temperature. 
A curve is given showing the internal energy of a gas-engine mixture 
in terms of the temperature. _ 
There is an appendix by Professor Callendar on ‘ The Deviation of 
Actual Gases from the Ideal State,’ and on ‘ Experimental Errors in 
the Determination of their Specific Heats.’ . 
The second report is mainly devoted to the subject of the specific 
heat of gases at high ‘temperatures... Regnault’s results at low tem- 
peratures “are discussed-in the light of Mr. Swann’s experiments, 
which were conimunicated to. the Committee by Professor Callendar. 
The Committee definitely adopted Mr, Swann’s values for air and for 
CO, as given below... - 
Volumetric heat of air at 100° C. is 19-8 lbs. per cubic foot, 
ce = CO, at 20° C. is 27-4 Ibs. per cubic foot, and 
at 100° C. is 30-7 lbs. per cubic foot. 
The results of the experiments made by Dr. Dugald Clerk with the 
object of determining the volumetric heat of air at high temperature 
are given in the report, together with a description. of Professor 
