ADDRESS. .. 9 
_ syphon-recorder, and the divided-ring electrometer, are illustrations of 
the valuable outcome of Thomson’s labours; the combination of the last- 
~ named instrument with sliding resistance coils has rendered possible the 
accurate subdivision of a potential difference into 10,000 equal parts. 
The general use of condensers in connection with cable signalling, due to 
Varley’s application of them for signalling through submerged cables 
with induced short waves, was instrumental in establishing the fact 
that all electro-static phenomena are simply the result of starting an 
electric current of known short duration round a closed circuit. The 
practical application of the Wheatstone Bridge led to numerous im- 
portant mathematical investigations, and induced Clerk Maxwell to devise 
a new mode of applying determinants to the solution of the complicated 
electrical problems connected with networks of conductors. The neces- 
sity for the universal recognition of an electrical unit of resistance led 
to the establishment, in 1860, of the Electrical Standards Committee of 
the British Association, whose long succession of important annual reports 
was instrumental in most important developments of theoretical elec- 
tricity, and, indeed, served to open up the whole science of electrical 
measurement. Matthiessen’s important investigations of the electrical 
behaviour of metals and their alloys, and the preparation and properties 
of pure iron, were the outcome of the commercial demand for a practically 
useful standard of electrical resistance, while Latimer Clark’s practical 
standard of electro-motive force, the mercurous sulphate cell, became in- 
valuable to the worker in pure electrical research. The unit of resistance 
established by the British Association Committee received, in 1866, most 
important scientific application at the hands of Joule, who, by measuring 
the rate of development of heat ina wire of known resistance by the passage 
of a known current, obtained a new value of the mechanical equivalent of 
heat. This value differed by about 1:3 per cent. from the most accurate 
results arrived at by his experiments on mechanical friction, a difference 
which eventually proved to be exactly the error in the British Association 
unit of resistance ; so that the true value of the unit of resistance, or Ohm, 
was determined by Joule fifteen years before this result was achieved by 
electricians. Clerk Maxwell’s remarkable electro-magnetic theory of 
light was put to the test, through the aid of the British Association unit 
of resistance, by Thomson, in determining the ratio of electro-magnetic 
unit to the electro-static unit of quantity. Many other most interesting 
illustrations might be given of the invaluable aid afforded to purely 
scientific research by the practical resuits of the development of electrical 
seience, and of the constant co-operation between the science student and 
the practical worker. No one could, more fitly than the late Sir William 
Siemens, have maintained, as he did in his admirable Address at our 
meeting in Southampton in 1882 that we owe most of the rapid progress 
of recent times to the man of science who partly devotes his energies to 
the solution of practical problems, and to the practitioner who finds relaxa- 
