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X. Intelligence and Miscellaneous Articles. 
ON THE EMPLOYMENT OF MARSH-GAS FOR PRODUCING EXCEED- 
INGLY LOW TEMPERATURE. BY M. CAILLETET. 
To the Editors of the Philosophical Magazine and Journal. 
GENTLEMEN, 
I HAVE just received the September Number of the Philoso- 
phical Magazine, in which I read with surprise a communication 
by Professor J. Dewar claiming the priority for employing marsh- 
gas in order to obtain very low temperature. Mr. J. Dewar, to 
rove his claim, alludes to a note published by him in ‘ Nature’ 
of the 4th of October, 1883, which, he says, “will prove that my 
experiments with liquid marsh-gas were made a year in advance 
of those made recently by M. Cailletet.” 
It is to be regretted that Mr. J. Dewar, who must be well 
acquainted with the contents of the communications presented by 
me to the French Academy of Sciences on the use of Marsh-gas, 
as well as the date of its presentation, has not spoken of the 
Notice I was obliged to publish a few weeks afterwards to refute 
the unjust claim of priority alleged by M. Wroblewski. This Note 
was deposited by me, closed and sealed, in the hands of the President 
of the French Academy on the 12th of December, 1881, that is to 
say, two years previous to the publication made by Mr. J. Dewar in 
‘ Nature. The Note was opened at my request and read in the 
Academical Meeting of the 4th of last August. It contains these 
words :—‘“ I am busy working up researches, at this moment, which 
will take me a long time, and will not be published before a 
lengthened period. I have been obliged to speak of the details of 
these researches to several persons; it is therefore quite necessary 
for me to establish early my rights to priority in case any author 
were to take precedence, and for that object 1 write this note, which 
contains the summary ot my work. I am trying to obtain greater 
cold than that obtained until now by scientific men..... 
‘“« By means of a pump, the piston-rod of which is covered with 
mercury, preventing thereby air and other injurious impediments, 
I can obtain the liquefaction of great quantities of carbonic acid 
and protoxide of nitrogen, as also of marsh-gas and ethylene, whose 
critical points are greatly inferior to those of carbonic acid. I 
am nearly certain to obtain very low temperature by plunging my 
instruments in these liquefied gases. I hope, lastly, to be able to 
liquefy oxygen, nitrogen, and other gases completely by refrigera- 
ting them by means of ethylene or marsh-gas boiling, after having 
compressed them in a curved tube by employing the instrument 
invented by me and which is well known to the Academy.” 
This Note cannot leave, I trust, any doubt of the priority of my 
researches over those of Mr. J. Dewar; and it is certainly owing to 
his not haying known it that he has published in the Philosophical 
Magazine the article which I feel entitled to answer. 
L. CatnLEeret, 
Paris, 10 décembre, 1884, Membre de ? Académie des Sciences, 
Phil. Mag. 8. 5. Vol. 19. No. 116. Jan. 1885. EF 
