RESISTANCE BY A METHOD BASED ON THAT OF LORENZ. 
33 
by Dr. Glazebrook. One of these coils was No. 3715, and its value in 1894 was 
stated by Dr. Glazebrook to be 1’00026 0 ohms (international) at 14°'95 C., the 
relation between the B.A. unit and the ohm (international) being taken as 
1 ohm = 1'01358 B.A. unit.* From the results obtained at the N.P.L. in 1908 we 
conclude that this coil increased in resistance in the interval 1894-1908 by 7 parts in 
100,000. Its value in 1908 was measured to be 1'00066 international ohms at 
16°'0 C. or 1'00034 international ohms at 14°'95 C. When allowance is made for the 
rise in resistance of 7 parts in 100,000, it will be seen that the difference from 
Dr. Glazebrook’s value is 1 part in 100,000. We conclude, therefore, that the value 
given by Viriamu Jones in 1894 is not in error because of any uncertainty in the 
values of the resistance coils used. 
Similarly we have investigated the coils used by Ayrton and Jones in 1897, and 
we find the values in Board of Trade ohms agree with the values in international ohms 
within 1 or 2 parts in 100,000. We conclude, therefore, that the length of the column 
of mercury representing the ohm is (from their experiments) j = 106*274 cm. 
Unfortunately, we are not sufficiently acquainted with the standards used by other 
investigators to reduce their results, and in the last column of the table the results 
given, except for the cases already dealt with, are those only in which mercury 
standards were available. 
Section 1.—Introductory. 
The instrument described in this paper is the outcome of a desire expressed by the 
late Prof. J. Viriamu Jones at a meeting of the British Association Committee on 
Practical Electrical Units and Standards, in 1893. Prof. Jones expressed the hope 
that in the near future there might be constructed an apparatus based on the method 
used by Lorenz, which would be kept in constant use in a national laboratory 
and embody in concrete form a proper ultimate standard of electrical resistance. 
In 1900 the Drapers Company of London promised to Prof. Jones the funds for 
the construction of such an instrument, and after Prof. Jones’s death in 1901 the 
Company placed £700 at the disposal of the Executive Committee of the National 
Physical Laboratory in order that the instrument might be made. 
The apparatus was to be in memory of Prof. Jones, and to be constructed under 
the superintendence of the late Prof. Ayrton and of Dr. Glazebrook. Delay in 
proceeding with the work arose owing to the construction of the Ayrton-Jones 
current balance, and it was not until after completion of the balance in 1907 that a 
start was made. Unfortunately, Prof. Ayrton was in very poor health, and 
although keenly interested in the work he did not live to take any part in it. 
The form of apparatus eventually decided on was considerably larger than 
anticipated in 1893. The metal work was much too heavy for machining in the 
* ‘ B.A. Elec. Stands. Committee Reports,’ 1892 and 1894. 
YOL. CCXIY.-A. 
F 
