AG 
final report, but hoped that the inherent difficulty and importance of the 
subject would sufficiently account for the delay. It can hardly be said 
that the final report has yet been forthcoming, as a committee with some 
of the original members in it still exists and reports regularly every year 
on valuable work done by it. The committee worked energetically for a 
number of years, not only on the standard of resistance, but on those of 
current, electro-motive force and capacity. It incidentally supplied a great 
deal of quantitative data on a number of subjects and particularly as to 
the permanency of alloys, the variation of their resistance with tempera- 
ture as depending on their composition, and so forth. In looking over the 
results of the early work of the British Association committee one is apt 
to indulge in adverse criticism. It is hard for many of the younger work- 
ers to appreciate the difficulties which are met in a first attempt. It would 
be equally just to congratulate ourselves that we have better marksmen 
to-day than there were fifty years ago, without making allowance for the 
modern rifle. 
The first absolute determination of resistance was probably that made 
by Kirchhoff about fifty years ago. Weber published his method in 1852, 
and then came the British Association’s determination by Maxwell, Stew- 
art and Jenkin in 1863. Neither of these were very exact, but they paved 
the way for the splendid exhibitions of experimental skill which followed. 
Among those to whom we are most indebted for this later work may be 
mentioned Kohlrausch, Rayleigh, Glazebrook, Rowland, Wiedemann, Mas- 
cart, etc. The greatest step in advance in recent years has been the in- 
yention of the revolving disc method by Lorenz of Copenhagen, and its 
subsequent improvement and application by himself and by J. VY. Jones. 
The determinations made by the latter by this method are probably al- 
most absolutely correct. 
A subject which has attracted much attention comes in incidentally here, 
namely, the electro-magnetic theory of light propagation suggested by 
Maxwell. According to this theory the ratio of the electro-magnetic unit 
of quantity of electricity to the electrostatic unit ought to be the same as 
the velocity of light. In 1868 a determination of this ratio was made by 
MecKichan under Lord Kelvin’s direction and gave close agreement with 
the theory. Since that time determinations have been made by various 
methods by Maxwell, Shida, Ayrton and Perry, J. J. Thomson, Rosa, 
Lodge, Glazebrook and others, with the result that the ratio of the two 
units does not differ from the velocity of light by as much as the probable 
