PKACTICAL STANDARDS FOR ELECTRICAL MEASUREMENTS. 55. 



With regard to tlie construction of the ampere balance the Committee 

 are sorry that they cannot report progress ; they have learnt with extreme 

 regret of Professor Ayrton's ill-health during part of the year, but are glad 

 to know that he believes he will be able to continue his investigations 

 into this important question, and they have therefore I'eason to hope 

 the matter will be advanced. 



In this work the late Principal Viriamu Jones was closely associated 

 with Professor Ayrton, and it is a source of great pleasure to the Com- 

 mittee to know that, through the generosity of the Drapers' Company, 

 his name and connection witli Electrical Measurements will be perpetuated 

 at the National Physical Laboratory. The Company had promised to 

 Principal Jones the funds for the construction of an improved Lorenz 

 apparatus for the determination of the ohm, and they have intimated to 

 the Committee of the Laboratory their intention to place TOO/, at the 

 Executive Committee's disposal for the construction of such an apparatus 

 in his memory under the superintendence of Professor Ayrton and the 

 Director of the National Physical Laboratory. The Secretary states that 

 steps have already been taken to obtain designs for the instrument. 



At the Meeting in Belfast Sir William Preece drew the attention of 

 the Commitee to the work of the Standardisation Committee of the 

 Engineering Societies, and expressed the hope that in his capacity as chair- 

 man of the electrical branch of that committee he might have the assist- 

 ance of the Electrical Standards Committee. The Secretary was instructed 

 to afford all the assistance in his power. 



Reference was also made to the definition of the unit of heat, and the 

 Secretary was requested, with the assistance of Mr. Griffiths, to draw up 

 an Appendix to the Report dealing with this. The Committee expressed 

 the strong hope that any unit of heat foi-mally accepted by engineers 

 should be based on the C.G.S. system of units. 



In conclusion the Committee recommend that they be reappointed, 

 with a grant of 151., to be used for the establishment of a standard 

 of capacity and for the construction of standard platinum thermometers ; 

 that Lord Rayleigh be Chairman and Mr. R. T. Glazebrook Secretary. 



APPENDIX. 



On the Definition of the Unit of Heat. 



The question of the definition of the unit of heat has been before the 

 Committee on various occasions. 



In 1896, at the Liverpool Meeting, after an exhausti^•e discussion and 

 the consideration of letters from scientific men in all parts of the world, 

 the following propositions were provisionally approved : — 



Fropositio7i I. — For many purposes heat is most conveniently measured 

 in units of energy, and the theoretical C.G.S. units of heat is one erg. The 

 name 'joule' has been given by the Electrical Standards Committee to 

 10^ ergs. 



For many practical purposes heat will continue to be measured in 

 terms of the heat required to raise a measured mass of water through a 

 definite range of temperature. 



If the mass of water be one gramme, and the range of temperature 1° C. 

 of the hydrogen thermometer from 9°-5 C. to 10°-5 C. of the scale of that 



