598 New Method of Determining J hernial Conductivity. 

 Or mean value of ^ — = 15574. 



This gives a mean value for K='0209. 



Each curve was drawn three times by an assistant and the 

 one lying intermediate between the other two accepted for 

 calculation of K. In such graphic methods a repetition by 

 different people, or even by the same person, leads to slightly 

 different results ; but in the present experiments, where the 

 size of the thermometer-bulbs must have an appreciable 

 effect on the uniformity of cross-section of the tube, it would 

 be out of place to use elaborate mathematical methods of 

 interpolation which will most probably be necessary in 

 future work. A general consistency for the value of K is 

 obtained using different velocities, and this value is of the 

 right order. 



(8) Conclusion. 



The curves obtained agree closely with those which can be 

 deduced from theory, and promise to lead to a new method 

 of determining thermal diffusivity directly. This method 

 has the advantage of requiring only temperature measure- 

 ments, quantity of heat not entering directly but being 

 inferred from a knowledge of specific heat. In improving 

 the method the first thing will be the substitution of thermo- 

 j unctions — at much more frequent intervals — for thermo- 

 meters. The cross-section of the tube need hardly then be 

 affected, and many more points on the curve could be 

 obtained, thus diminishing very much errors in graphic 

 interpolation. 



The author is, however, presenting his research at this 

 stage, embracing the theory and the work which can be done 

 with thermometers, as he is anxious to perform experiments 

 under the best possible conditions, and hopes to receive 

 advice and criticism before proceeding with more delicate 

 work. 



The author wishes to express his thanks to the Principal 

 and Council of Birkbeck College for facilities for carrying 

 out the work, and more especially to Dr. A. Griffiths who 

 has watched the work with interest from the beginning and 

 has given valuable help and encouragement throughout. 



