152 Intelligence and Miscellaneous Articles. 
I gave up to 430 atmospheres to have them at the normal 
pressure. 
For pressures above 430 atmospheres we may obtain exact results 
by using hydrogen. I have in fact shown that for this gas the 
curve representing the values of pu is a straight line; we may 
without hesitation prolong this line to far higher pressures ; this 
is what I am doing in researches in which I have worked under 
pressures of several thousand atmospheres, and of which I shall 
before long give an account to the Academy.—Comptes Rendus, 
December 8, 1884. 
ON GAS-ENGINE INDICATOR-DIAGRAMS. 
To the Editors of the Philosophical Magazine and Journal. 
Siemens Brothers and Co., Limited, 
Telegraph Works. Woolwich, Kent,. 
GENTLEMEN, January 16, 1885. 
I enclose a letter from Professors Ayrton and Perry correcting 
a previous paper of theirs, for which I presume you will find room 
in your next publication. Yours truly, 
F. Jacos. 
Technical College, Finsbury, E.C., 
Dear Sir, October 9, 1884. 
Mr. F. Jacob, in a letter addressed to Dr. Guthrie and fowarded 
to us, has kindly drawn our attention to the fact that the method 
of observation of loss of heat described by us in the Postscript to 
our paper “On Gas-Engine Indicator-Diagrams,” and which was 
used in obtaining the results referred to in the postscript, 1s not, 
as we thought, new, having also been used by the late Sir W. 
Siemens, and described by him in his paper “On the Dependence 
of Radiation on Temperature,” read before the Royal Society on 
April 26, 1883; to whom of course we hasten to cede the priority. 
We may add that Mr. J. T. Bottomley, in his paper just pub- 
lished in the Proceedings of the Royal Society, “On the Permanent 
Temperature of Conductors through which an Electric Current is 
passing ” &c., has also described the use of the same method, and 
he tells us that he, like ourselves, was unaware of Sir W. Siemens’s 
paper. Weare, &e., 
W.E. Ayrton, 
JOHN PERRY. 
