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Jf 
ON THE CONSERVATION OF MASS. 
By J. JOLY, D.Sc., F.R.S., F.G.S., Professor of Geology in the University of Dublin, 
Hon. See., Royal Dublin Society. 
(Puatre VY.) 
[Read January 20, 1903. ] 
THE recent publication of a memoir by A. Heydweiller, ‘‘ Ueber Gewichtsiinde- 
rungen bei chemischer und physikalischer Umsetzung,”’* has again raised the 
question of a possible alteration of weight attending certain chemical and physical 
changes. The paper has been closely criticised; but up to the present no common- 
place explanation of the results has been suggested. The most serious criticism 
is to be found in the dynamical difficulties which have been shown to attend the 
acceptance of the conclusion arrived at by the experiments.t 
As to the experimental details of Heydweiller’s work, the reader of his paper 
feels inclined to ask why so many possible sources of error were left to evaluation 
and not removed by suitable arrangement of the apparatus. ‘The density and 
hygrometric state of the atmosphere are capable of elimination as factors in com- 
parative experiments of the kind by exhaustion of air from the tubes containing 
the reacting substances, air-tight closing of the balance and proper drying of the 
contained air. ‘The necessity of handling the tubes is again avoidable; although 
Heydweiller’s balance did not, as he states, permit of arrangements to effect this. 
But while it is possible to plan experiments of a more direct character, we cannot 
on this account refuse to attach value to Heydweiller’s results. It is difficult to 
suggest how a systematic error such as would be required to account for his results, 
can have entered his experiments. 
A large part of the little we know of the physics of mass and weight may be 
comprised in the statement that the masses of bodies are proportional to their 
eravities. If this is not strictly true, or if the connexion breaks down under 
certain conditions of intermolecular actions, we are apparently at liberty to 
speculate on many far-reaching consequences. It must be admitted that some 
of the most remarkable of these are not contrary to our experience when 
* Annalen der Physik, Bd. 5, 1901, 394. + Lord Rayleigh in Nature, vol. Ixvi, p. 58. 
TRANS. ROY. DUB. SO0., N.S., VOL. VIII., PART Il. EF 
