56 REPORT— 1888, 



have been compared with each other by the Secretary and Mr. T. C. Fitz- 

 patrick ; an account of the experiments is given in an appendix to the 

 report, togfether with a chart giving the values of their resistance between 

 10° and 20°. The general result of the comparison is that with two 

 exceptions the relative values of the standards between the tempera- 

 tures of 10° and 20° have not seriously changed since they were con- 

 structed in 1865 until June 1888. A change of about "0002 B.A. Unit 

 has been observed in the coil F since the end of June 1888. 



The attention of the Committee has been directed by several practical 

 electricians to the desirability of a redetermination of the value of the 

 specific resistance of copper. It is known that copper wire is now made 

 having a resistance 3 or 4 per cent, less than Matthiessen's standard. 



In view of the importance of copper to electricians the Committee 

 have undertaken to make experiments on the specific resistance of copper, 

 and wish to thank the various gentlemen, who have brought the matter 

 forward, for their offers of help. 



At the last meeting of the Committee it was resolved, on the motion 

 of Mr. W. H. Preece, to adopt the name ' Therm ' for the Gramme-Water 

 Degree Centigrade Unit of Heat. 



Thus one ' Therm ' is the quantity of heat required to raise one 

 gramme of water at its maximum density one degree Centigrade. 



It was also agreed to adopt the name ' Joule ' for 10^ C.G.S. units of 

 work. Thus a Joule is equal to 10^ ergs. It is the work done in one 

 second by the power of one Watt, or again the work done when a 

 current of one Ampere flows for one second between two points between 

 which the difi'erence of potential is one Volt, and hence a power of one 

 Watt is one Joule per second. 



Hence, also, if we take the value of the mechanical equivalent of heat 

 as 42 X 10^ ergs, we have 



1 Therm=4-2 Joules. 



In accordance with a suggestion made at the Manchester meeting the 

 value of the resistance of mercury in terms of the B.A. Unit has been 

 again determined by the Secretary and Mr. Fitzpatrick.^ 



They find that a column of mercury 1 metre long 1 sqr. mm. in 

 section has at 0° C. a resistance of -95352 B.A. Unit, and that the value of 

 the ohm in centimetres of mercury is 106"29. 



The Committee are of opinion that they should be reappointed, with 

 the addition of the name of Mr. T. C. Fitzpatrick, to continue the experi- 

 ments already referred to ; they ask for a grant of 1001. They propose 

 that Professor G. Carey Foster should be the Chairman and Mr. R. T. 

 Glazebrook the Secretary. 



Appendix. 



Ow the Permanence of the Original Standards of Resistance of the British 



Association and of other Standard Coils. By R. T. Glazebrook and 



T. C. Fitzpatrick. 



The original standards were compared together by Messrs. Matthiessen 



and Hockin in 1865 and 1867, by Messrs. Chrystal and Saunder in 1876, 



by Dr. Fleming in 1879-81, and by the Secretary and Mr. Fitzpatrick in 



1887-88. The details of Dr. Fleming's observations have never been 



' Proc. Royal Soc. vol. xlir. ; Phil. Trans. 1888. 



