CRITICISM. 21 



and Joule at Manchester proclaimed that the work done by any quantity 

 of water falling there a distance of 772 feet is capable of raising that water 

 one degree Fahrenheit. ' Here seemed something definite. To measure 

 temperature by mass and velocity, to measure a degree by the flight of a 

 stone, or the heat in the human body by the fall of a factory chimney if 

 rather roundabout and elusive of the main question seemed at any rate 

 promising of exact results ! Unfortunately the difficulty was to pass from 

 the theory to its application. The complicated nature of the problem, 

 the " imperfection " of the gases and other bodies under consideration, 

 the latent and specific heats to be allowed for, the elusive nature of heat 

 in experiment, and the variable value of the degree itself all render the 

 conclusions on this subject most precarious ; and the general equations 

 connecting the Fahrenheit or other temperatures with a thermo-dynamic 

 scale while they become so unwieldy as to be practically useless are 

 themselves after all only approximate. 



Finally, to give a last form to the mechanical theory of heat, the con- 

 ception of flying atoms or molecules was introduced, and a number of 

 neat generalisations were deduced from dynamical considerations. Of 

 course it was inevitable, having once started with a mechanical theory, 

 that one should arrive at the Atom some time or other and (from what 

 has already been said) it was also inevitable that the result should be 

 unsatisfactory. It is sufficient to say that the molecular theory of heat is 

 not in accordance with facts. Such things as the law of Charles and the 

 law of Boyle, which according to it should be strictly accurate and of 

 general application, are known to be true only over a most limited range. 

 This failure of the theory may be said to arise partly from its being pur- 

 sued by the statistical method ; but if, on the other hand, we were to try 

 and follow out the individual movement of each molecule, we should be 

 landed in a problen far exceeding in complexity the wildest flights of 

 Astronomy and should have exchanged for the original difficulty about 

 ' ' temperature " a difficulty far greater. 



The result of all this has been that notwithstanding the talk about 

 energy and atoms, Science has sadly to confess that it can still give no 

 valid meaning to the word temperature : the unknown thing is still un- 

 known, the independent existence round the corner still escapes us. By 

 the very effort to arrive at something independent of human sensation, 

 Science has, in a roundabout way, arrived at an absurdity. When the 

 man said he was cold, his statement deplorably vague as it was had 

 some meaning : he was describing his feelings, or possibly he had seen some 

 snow or some ice on the road ; but when, in the endeavor to leave out 

 the human and to say something absolute, Science declared that the 

 temperature was thirty degrees, it committed itself to a remark which 



i A statement obviously applying from what has been already said at only one 

 point in the scale. 



