102 REPORT—1890. 
Taste VI.—Results for ¢, 101. 
Sts dusedin | Tem- Value Valueon Chart!) y-~ | 
Date agg eos | perature | found in 1885, 1886 Difference 
Feb. 1887 F 16:3 *99970 “99930 “00040 
Nov. 1889 G 15:9 “99955 "99920 “00035 
> 5 15°1 *99932 “99899 ‘00033 
a 5 16:0 ‘99955 "99922 00033 
Dec. 1889 Flat 14-4 “99909 “99880 ‘00029 
~ 15-0 *99925 “99897 -00028 
3s 23 13°3 “99879 “99850 “00029 
A= _ 76 "99725 ‘99695 “00030 
wen = 65 | “99701 +99668 00033 
These tables show three facts conclusively: (1) That up to December 
1889 no appreciable change had taken place in the relative values of 
G, 100—the Legal Ohm Standard—and Flat or G; (2) that between 
J anuary 1886 and February 1887 ¢, 101, which had varied pre- 
viously, changed by about ‘0004 ohm; and (3) that the greater part of 
that change has remained permanent up to December 1889. At present 
the difference between ¢, 100 and , 101 is about ‘0004; in 1886 it 
was about ‘0008. The agreement between the observations in November 
and December 1889—in one set of which Flat was the standard of com- 
parison, while in the other G was used—show that the relative change in 
G and Flat took place after this date. 
APPENDIX II. 
On the Air Condensers of the British Association. By R. T. GLazeBRoox 
(with a Note by Dr. A. MurrueaD). 
The question of issuing certificates of capacity has from time to time 
been discussed by the Committee. The following paper gives an account 
of some experiments that have been in progress during the past two 
years with this object in view. 
In the Report for 1887 the Committee express the opinion that it is 
desirable to proceed with the construction of an air condenser. In con- 
formity with this opinion a meeting was held in London, at which Dr. A. 
Muirhead exhibited an air condenser consisting of a series of concentric 
brass cylinders insulated by glass rods, which appeared to the Committee 
to possess great merits; and it was decided that the Secretary should 
test this and two similar condensers which Dr. Muirhead offered to lend, 
before proceeding further with the construction of condensers for the 
Association. The tests were carried out with satisfactory results. 
The capacity of each condenser was determined repeatedly, using the 
method of a vibrating commutator, due to Maxwell, already employed by 
J. J. Thomson, ‘Phil. Trans.,’ 1883, and Glazebrook, ‘ Phil. Mag.,’ 
August 1884. The values found were :— 
C, = :0030514 microfarad. 
C, = 0031258 s9 
C3 = 0053288 Ps; 
