76 
PROFESSOR HUGH L. CALLENDAR ON 
Value of No. 4086 from Observations at the National Physical Laboratory. 
Date. 
Temperature. 
Value from 3715. 
Temperature. 
Value from “Flat.”* 
July 20. 
o 
25-0 
1-00067 
0 
24-9 
1-00067 
„ 26. 
24-4 
1-00072 
24-4 
1-00059 
,,28. 
21-4 
1-00063 
21-3 
1-00059 
,,28. 
21-6 
1-00062 
— 
— 
„ 30. 
18-9 
1-00057 
— 
— 
August 1. 
16-0 
1-00045 
— 
— 
These observations give a mean value of 1 '00061 ohms at a temperature of 
21°‘96 C., and indicate a temperature coefficient of about ‘000027 for changes taking- 
place in a few days. This result is inconsistent with the value (5) 1‘00037 at 
21°‘74 C. found by Barnes, unless we suppose the temperature-coefficient employed 
by Barnes for the Pt-Ag coils to be a little too small, or unless No. 4086 had 
increased in value on its journey from Canada. Mr. Glaze brook was not perfectly 
satisfied with these observations, as the temperature was too high and variable, and 
the difference to be measured on the Pt-Ir bridge-wire, as well as the temperature 
correction of the standards, was rather large. He therefore repeated the observations 
in December, at a lower temperature, under much steadier conditions, with the 
following results :— 
Value of No. 4086 from National Physical Laboratory Standards. 
Date. 
Temperature. 
Value from 3715. 
Temperature. 
Value from “ Flat.” 
December 13, 1900 . 
o 
12-1 
1-00018 
o 
11-9 
1-00020 
,, 18 and 19 . 
13-2 
1-00016 
13-0 
1-00018 
„ 20 ... . 
11-3 
1-00016 
11-5 
1-00015 
„ 21 ... . 
12-1 
1-00017 
12-1 
1-00015 
„ 28 ... . 
10-3 
1-00010 
— 
— 
The results of these observations give a mean value of 1'00016 at a temperature of 
12°‘0 C. This appeared inconsistent with the July observations. It was also much 
lower than the value (6) 1 *0004 L at 14°‘8 found bv Fraser, unless we suppose either 
that the coefficient ‘000254 applied by Barnes to the platinum-silver coils was too 
small, or that No. 4086 had fallen in value in the interval. 
* “ Flat ” is one of the original B.A. unit standard coils belonging to the British Association, the 
temperature coefficient of which is taken to be -000277, as determined by Fleming in 1876. 1 ohm is 
assumed to be 1 01358 B.A. unit. No. 3715 is a more recent standard ohm. 
