234 The N.Z. Journal of Science and Technology. [Jan. 
It is not surprising, therefore, that when it was realized that the 
phenomena of electricity and magnetism involved the existence of a medium 
between the electrified or magnetized bodies through which the action of 
one electrified or magnetized body upon another could be transmitted—it is 
not surprising that the already postulated ether of light should be examined 
to see how far the properties already assigned to it were sufficient also to 
account for electro-magnetic phenomena—or, rather, for their tranmission 
from place to place. It is to James Clerk Maxwell, the first Cavendish 
Professor of Physics at Cambridge (Sir E. Rutherford is the fourth), that 
we owe much of what we know, and to whom we are indebted for many 
most fertile suggestions for research and investigation—researches which, 
conducted by many persons, of the most diverse nationalities, have extended 
from Maxwell’s time (1875 or thereabouts) until to-day. 
There are two well-known systems of electrical units which have 
gradually evolved as men’s minds became clearer upon electrical and 
magnetic questions. One of these is based essentially on the phenomena 
of electricity at rest, and is known as the electrostatic system. By con¬ 
sidering what happens in the neighbourhood of insulated electric charges, 
and the laws of these happenings, a complete and scientific system of units 
has arisen. Another system has come about—equally fundamental and 
essential—which is derived from the laws of electricity in motion. This 
system is known as the electro-magnetic system. Now, it is to Maxwell 
that we owe the prediction that a comparison of the same quantity measured 
in each of these systems involved (if his ideas were right) the speed with 
which an electric impulse was propagated through the medium which 
conveyed its effects. Maxwell contended that this medium was that which 
also conveyed light; and, if so, by measuring the same electrical quantity 
in each system of units an evaluation was possible of the speed of light. 
Could any confirmation be more satisfactory ? For here was the possi¬ 
bility of measuring the velocity of light without using any optical instrument 
whatever in the measurement—that is to say by purely electrical measure¬ 
ments. The measurements were made both by Maxwell and also by his 
successor at Cambridge, Lord Rayleigh, and the resulting velocity of pro¬ 
pagation of the electrical impulse turned out to be exactly the same as that 
which had been previously obtained for the speed of propagation of waves 
of light. The agreement is remarkable, and the confirmation of Maxwell’s 
views was complete. 
But arising from Maxwell's work other developments were not long in 
coming. Maxwell predicted that under certain circumstances it would be 
possible to excite electro-magnetic waves which would differ from the waves 
of light only in that they were longer. They should be propagated with 
the same, or very nearly the same, velocity—viz., 186,000 miles a second. 
They would not be seen, as are the waves of light, for only waves of a 
wave-length between very definite limits affect the eye ; but they should 
be detectable by other means, when such means were discovered. At 
the time that Maxwell wrote (1875) the means were not discovered, but 
they were in 1899 by Hertz. Investigation and research has, since very 
greatly improved the methods of exciting and detecting the aves, and' 
they are now commercially used in wireless telegraphy. Thus wireless 
telegraphy and all that it means and implies is the direct outcome through 
three centuries of speculation and research, both of a mathematical and 
experimental kind, of man’s belief in an ether. And every means by which 
the velocity of a disturbance through it had been measured had given 
practically the same velocity—viz., 186,000 miles a second. 
