96 REPORT— 1905. 
immediately afterwards. The four coils of bare copper wire wound on 
marble cylinders have given complete satisfaction, the ellipticity and 
conicality of each being very small. The average ellipticity is such that 
the diameters of the ellipse differ in length by about 10 micron, while the 
average conicality is approximately represented by a difference between 
the mean diameters of two sections 13 cm. apart (the axial length of one 
coil) of about 12 micron. The contour of the cylinders is very well 
known, and the mean diameter has been measured with a probable error 
not greater than 0-001 per cent. This knowledge enables the calculation 
of the mutual induction between two coils to be made with great 
accuracy. 
Preliminary observations with a current of nominal value 1 ampere 
were made at various times during April and May, the first set of such 
observations determining the temperature to which the coils are raised 
by a continuous steady current, the magnitude of the disturbances 
arising from convection currents, the influence of the silver strips, and 
the nature of other disturbances. The convection currents give some 
trouble, but the experiments already carried out indicate that a change 
of 0-001 per cent. in a current of nominal value 1 ampére will be 
detectable. 
The balance acts conveniently as an indicator of the magnetic 
permeability of the marble and metal parts of which it is constructed, 
and it is satisfactory to know that the permeability of these parts does 
not differ from unity by a measurable amount, and cannot therefore 
influence the final results. 
Early observations showed that the concentric cable employed in the 
leads to the balance was faulty, some of the internal strands being broken, 
and the variable contacts thus resulting prevented a steady current from 
being obtained. Fresh concentric cable is being inserted, which should 
enable the final observations to be speedily made. 
Apparatus for the determination of ‘g.’—The three half-second 
pendulums (the property of the Board of Education, and which were 
used in the last Antarctic expedition) have been swung at Kew and at 
the National Physical Laboratory in the room where the balance is 
erected. The observations are being continued. 
When all the constants have been determined and the observations 
with the balance are complete it will be necessary to consider the means 
by which the result is to be given to the world. The current may be 
reproduced either by means of the silver voltameter or by means of a 
standard cell and a standard resistance. The silver voltameter is being 
investigated at the National Physical Laboratory, and a comparison of 
the accuracies of reproduction would perhaps influence the choice. 
The Committee were represented at the International Electrical 
Congress at St. Louis last year by Professor Perry and the Secretary. 
The resolutions passed at the Cambridge Meeting of the Committee 
(see Report for 1904) as to certain questions proposed for discussion 
were laid before the Congress, and after discussion the following reports 
were unanimously accepted :— 
Commitice of the Chamber of Delegates on International Electr'o-magnetic 
Units. 
The Sub-Committee appointed September 13, 1904, beg leave to suggest that the 
Chamber of Delegates should adopt the following report ;— 
