232 The N.Z. Journal of Science and Technology. [Jan. 
RELATIVITY.* 
By Professor C. Coleridge Farr, D.Sc., F.P.S.L., F.N.Z.Inst., Canterbury 
College. 
Though sprung upon the world with such dramatic suddenness, relativity 
has in reality been a very gradual growth in the minds of men, and the 
world has been slowly but surely tending towards either this or some other 
satisfactory solution of its difficulties for very many years. The pheno¬ 
menal advances which have been made in scientific thought and method 
during the closing years of last century and the opening ones of this one 
have brought these difficulties into greater prominence, and have emphasized 
them in such a way that had not Einstein arisen some other genius must 
inevitably—though perhaps much more slowly—have guided the thoughts 
of men into the paths which he has trodden ; for Einstein’s work, most 
brilliant as it certainly is, is but the fitting and inevitable outcome of a 
long series of investigations and speculations which commenced about three 
hundred years ago, at the time of Descartes, in whose writings may be seen 
the first glimmerings of the ideas that subsequently developed into the 
conceptions which we now have of the interstellar medium known as the 
luminiferous ether. 
Of this medium, its history, and the evidence for its existence, it will 
be necessary for me to speak at some length, so that you may realize on 
what grounds we have asserted so boldly that there is an ether, and what 
modifications in those conceptions have been brought about by these recent 
relativity developments—-what, in short, is the present position of thought 
upon the subject. 
Until the seventeenth century the only influence which was known to 
pass from star to star was light, an influence whose laws and general 
phenomena were at that time—and, indeed, until much later—practically 
unknown. Towards the end of that century Newton added the influence 
of gravitation to that of light, and experiments made mainly during the last 
hundred years have made the further additions of electric and magnetic 
attractions. 
It was to explain the first of these phenomena—viz., the phenomenon 
of light—that the necessity for an interstellar medium first impressed itself 
upon the minds of thoughtful men. It was found necessary to imagine 
space to be filled with this medium, which acts as the conveyer of light 
from place to place and from star to star. The ether is, indeed, the solitary 
tenant of the universe, save for that infinitesimal fraction of space which 
is occupied by what we call ordinary matter—and this is possibly only some 
peculiar manifestation of the same all-filling plenum. 
Having thus in a preliminary kind of way, and perhaps tentatively, 
decided that light was transmitted from star to star by this (at that time) 
more or less hypothetical medium, men slowly began to turn their attention 
to a consideration of the laws and phenomena of light, and to build up 
from them a picture of what the nature and properties of this medium must 
be. At the time of which I am thinking—Descartes’ time—The law that 
* An address delivered to the Canterbury Philosophical Institute on the 7th August, 
1920. 
