122 DR- K. H- GRIFFITHS AND MR. EZER GRIFFITHS ON THE 



coil R ; *J = 4'184x 10' ; and Q, the number of thermal units lost or gained during 

 time t from sources other than the electrical supply. 



In these experiments the values of fy and a were so arranged that Q was in every 

 case small or negligible, and, if necessary, could be estimated with sufficient accuracy. 



7. With two exceptions, the samples of metals used were supplied by Messrs. 

 Johnson and Matthey, to whom we wish to express our sincere thanks for the trouble 

 they have taken in the matter. Their certificate concerning the degree of purity is 

 in each case appended. Information regarding the remaining metals (Cu and Fe) 

 will be found in the sections dealing with those two elements. 



8. Experiments on identical samples at the same temperature were repeated under 

 very varied conditions, in order to enable us to detect unsuspected sources of experi- 

 mental error. Two separate methods of experiment, involving different data and 

 methods of reduction, were employed. Three different sets of differential platinum 

 thermometers were used. The rate of heat supply was varied in the ratio of 9 : 1. 

 The determination of S at a given temperature with a particular sample was in several 

 OMOO repeated after the lapse of some months ; the quartz tubes and cover were 

 replaced by others of different masses &c. We were thus enabled to ascertain causes 

 of error which would otherwise have remained undetected (see p. 139). 



9. The results of our observations have been deduced from the actual experimental 

 numbers and in no case from " smoothed curves." 



The most serious difficulty presented by this method of experiment is that of 

 determining the mean temperature of the block of metal when its temperature is 

 altering. Temperature gradients must necessarily exist, since equalisation of 

 temperature by stirring is an impossibility. The manner in which this difficulty was 

 surmounted is described in later sections. 



When embarking on this investigation we proposed to extend our range of tempe- 

 rature to the lowest point obtainable by means of liquid air, limiting the inquiry to 

 the study of two or three metals only. Owing, however, to delay by the contractors 

 in the delivery of the liquid-air plant, we were compelled to postpone that portion 

 of our investigation dealing with temperatures below C. to a later date, and 

 therefore enlarged the scope of our inquiry so as to include the following metals, 

 namely, Aluminium, Iron, Copper, Zinc, Silver, Cadmium, Tin and Lead. 



As the data already accumulated concerning the capacity for heat of these metals 

 over the range C. to 100 C. may be useful to other obsorvers, we see no reason for 

 delaying the publication of the work already completed. 



SECTION II. 



Outline of Apparatus and of the Method of Experiment. 

 A diagrammatic sketch of the apparatus within the tank is indicated in fig. 1. 



f FK this value of J ' see P- no 



of Energy,' by E. H. GRIFFITHS (Camb. Univ. Press). 



