FRE SIDENTIAL ADDRESS. IN SEGTIO 
(Astronomy, Mathematics, Physics and Mechanics). 
THE PRESENT STATE OF ELECTRICAL KNOWLEDGE; 
By RICHARD THRELFALL, M.A., 
Professor of Physics, University of Sydney. 
A piscussion of the present state of electrical knowledge natu- 
rally involves an apology. .It is not without a certain amount of 
trepidation that I venture to address you on the most profound 
of physical subjects, nor should I have done so unless it had been 
suggested to me by the Secretary of the Association. Anyone 
with any knowledge of the matter will, I think, bear me out 
when I say that the difficulty of turning the results of mathe- 
matical reasoning into a form in any way suitable for an address 
is exceedingly grave, and should really be only attempted by 
those who have a special knowledge, to which I in no way 
pretend. I hope, however, that any account, however feeble, 
will not be altogether useless, since the mathematical thicket 
must have appeared impenetrable to many who would otherwise 
have taken an interest in the subject. A knowledge of the 
elementary facts of the subject will be assumed. Coming to 
the point with all convenient speed, I will give a sketch of 
Maxwell’s theory, because it has recently received what must be 
regarded as a great deal of striking confirmation. I will then go 
on to develop some of the arguments in favour of the theory, and 
will finally try to bring it up to date with respect to several 
points that have been more or less passed over in the genera] 
discussion. 
It is to Faraday that we owe the experimental foundation of 
the theory, as well as the fundamental step of the theory 
itself, the direction of attention to the properties of the space 
surrounding charged or conducting bodies, rather than to the 
bodies themselves. The ideas of Faraday were first put in a 
precise manner by Maxwell, and then extended so as to give rise 
to a theory of optics known as the electro-magnetic theory—one 
of the most brilliant concepts of physical science. An immense 
amount of detail was also added by Maxwell, both with respect to 
phenomena falling clearly within the limits of the theory, and also 
with respect to certain outstanding phenomena which were not so 
clearly accounted for. The exact description of the theory of many 
