282 Mr. H. F. W. Burstall on the Measurement 





of the T*, and those, on the other hand, of the "t**, may 

 possibly be identical. In fact, it is found that the values of 

 t* are practically identical for benzene, chloroform, and 

 carbon tetrachloride, being equal to about *70. For water, 

 aceton, and carbon bisulphide t* seems to be somewhat 

 higher, whereas for ether it is much lower : such results, 

 however, do not seem to deserve much confidence. Still, if 

 we assume for a moment t* for hydrogen to be '75 say, we 

 find —242° for T* ; and then the second point of inversion 

 ought to lie somewhere between that temperature and the 

 critical, that is, — 232°. 



XXIII. The Measurement of Cyclically Varying Temperature. 

 By Henky F. W. Bukstall, M.A., A.MJ.C.E* 



[Plates I. & II.] 



I HAVE been engaged since the latter end of 1892 in 

 attempting the measurement of the temperatures reached 

 in the cylinder of a gas-engine, and the following paper 

 embodies the results w 7 hich I have obtained. 



So far as I am aware no experiments on this subject have 

 been previously published ; such attempts as have been made 

 have failed from the want of a sufficiently sensitive thermo- 

 meter. The platinum resistance-thermometer has, however, 

 proved to have the required sensitiveness, and I shall devote 

 this paper to the description of one of its forms which I have 

 found suitable for the measurement of cyclically varying 

 temperature. 



The direct determination of the temperature in the cylinder 

 clears the field for more complete discussion of the theory of 

 the gas-engine, but as I would rather treat the experiments 

 which I have already made as preliminary only, I will not 

 enter into any discussion on this point in the present paper. 



I had hoped during this work to have had the collaboration 

 of Prof. Kapper, but unfortunately, owing to the pressure of 

 other work, he was unable to devote the necessary time to 

 these researches. I wish to take this opportunity of thanking 

 him for putting at my disposal the experimental gas-engine at 

 King's College, and also for many valuable suggestions he 

 has made during the course of the work. 



The engine used is an Otto cycle-engine. This cycle, which 

 is that now most generally used in internal combustion-engines, 

 is completed in four strokes of the piston. 



* Communicated by the Physical Society : read June 14, 1895. 



