432 Mr. E. H. Griffiths 



on 







due in some measure to a comfortable belief in the validity 

 of any conclusions arrived at by Regnault. The disciples of 

 science are often accused by the public of a lack of reverence 

 for tradition and authority, but my own experience leads me 

 to the belief that no class is more conservative. If the name 

 of a master of our craft is at any time associated with some 

 conclusion or numerical value, even his own subsequent cor- 

 rections and amendments are liable to pass unregarded. 

 Numerous instances could be cited : as, for example, the 

 result of Joule's own comparison of his thermometer with 

 Rowland's ; or, again, Regnault's statement of his doubts 

 concerning his conclusions as to the Latent Heat of Evapo- 

 ration of Water at low temperatures. 



Our feelings of veneration for great men and our admiration 

 of their work are, however, carried to harmful excess when 

 they act as a check on the criticism and revision of the nume- 

 rical results of their experiments. Since the year 1879, when 

 Rowland published his monumental work on the mechanical 

 equivalent, there can, I think, be no doubt in any un- 

 biassed mind that Regnault's expression for the capacity 

 for heat of water is inaccurate at temperatures below 30°. 

 Yet we find the most recent books of reference ignoring the 

 researches of Rowland, and still reducing thermal quantities 

 to that impossible unit " the capacity for heat of water from 

 0° to 1° " by means of Regnault's formula. 



My object in the first part of this paper will be to show how 

 vague and uncertain is our knowledge of the changes in the 

 capacity for heat of water as its temperature varies. I shall 

 not attempt to consider at any length the work of all the 

 investigators who have attacked this problem, but shall be 

 guided by one general principle in my selection ; viz., that 

 however admirable the methods of experiment, or however 

 sound the theories on which they are based, the numerical 

 results are useless unless the observer has devoted sufficient 

 attention to the measurements of temperature. The force of 

 this argument will be more evident when it is remembered 

 that the experiments which give the most rapid decrease in 

 the capacity for heat of water at low temperatures (viz. those 

 by Rowland) would show an increase if the results were 

 expressed on the mercury- instead of the air-scale. It might 

 appear from this statement that if the changes are so small 

 they may be unimportant ; but it must be borne in mind that 

 in the reduction of the thermal quantities we have, as a rule, 

 to deal with the summation of such changes over large ranges 

 of temperature (as, for example, in "the method of mix- 

 tures"), hence the effect may be, and often is, considerable. 



