* MR, H. TOMLINSON ON THE INFLUENCE OF STRESS 
domain of physical science; but, though much has been done, very much more remains 
to be done, and a wide field lies open before us which cannot fail to richly reward the 
patient explorer. I write patient explorer advisedly, because, in many cases, any 
difference of molecular disposition which we can effect with the means at our disposal, 
produces only a very minute alteration in that particular physical quality which we 
may be examining, and an alteration which we can only hope to measure accurately 
by the exercise of a large amount of perseverance and conscientious labour. But 
whether the effect to be observed be large or small, there is no doubt that further 
investigations of the kind here indicated must be made ere we can gain a true insight 
into the nature of the action of physical forces or into any relationships which may 
exist between them. 
I proposed to myself, therefore, to examine as far as possible each of the various 
physical properties of one and the same specimen of different kinds of matter ; and, 
further, to investigate the alterations which can be jmoduced in these properties by 
stress and strain; being convinced that, by so doing, much light would be thrown on 
such subjects as electrical conduction, magnetic induction, thermal conduction and 
expansion, thermo-electricity, specific heat and elasticity. The words “stress” and 
“ strain ” are here used in their widest sense as intending to denote respectively the 
equilibrating application'" of any physical force, and the definite alteration of form or 
dimensions experienced thereby by the matter acted on by the force. 
In furtherance of the above-mentioned objects I procured some 60 feet of wire made 
of each of the various metals in common use, and also of the rarer metals, silver and 
platinum, and of the alloy platinum-silver, the three last in a state of chemical purity, 
and proceeded to determine one after the other the various physical constants of each. 
In consequence of the extensive scope of these researches, several of the various 
parts into which the paper is divided are far from being as complete as I could wish, 
and hope at some future period to make them; but I venture to present them as they 
are to the Society, as tending to show still further than has hitherto been done the 
“correlation of the physical forces,” and the value of this mode of investigation 
wherein one experiment immediately suggests several others. 
PART I.—MODULI OF ELASTICITY. 
“Young’s Modulus.” 
Description of apparat us. 
The values of “ Young’s modulus ” for the various metals were determined by a 
method devised by Sir W. Thomson.! Wires of the same material and diameter are 
suspended in pairs about 1 inch apart from each other, and are attached by one 
* ‘ Brit. Encyc.,’ Art.: “Elasticity,” p. 24. 
t Proc Roy. Soc., vol. xxix., p. 221. 
