where represents a particular species of mathematical operation. In ordinary language, these last two equations connote that varying electric and magnetic intensities will be propagated through the ether in wave form with a velocity , where is a magnitude yet to be determined. This discovery removed all possibility of action at a distance, since the field perturbations now appeared to be propagated from place to place with a finite velocity. It was, of course, of interest to determine the precise value of . The most obvious means would have been to create electromagnetic disturbances and then measure their speed of propagation directly. Physicists, however, were unable, in Maxwell’s day, to devise a means of performing such delicate experiments. But there existed another way of determining the value of . Maxwell remarked that it would be given by the ratio of the magnitude of any electric charge, measured successively in terms of electrostatic units (based on electricity) and then of electromagnetic units (based on magnetism).[41] Precise measurements conducted on electrified bodies and magnets then proved that the value of this ratio was about 186,000 miles per second; whence it became necessary to assume that periodic perturbations in the strains and stresses of the field would be propagated in the form of waves moving through the ether with this particular speed. But this velocity was precisely that of light waves propagated through the luminiferous ether. [Pg 128] The conclusion was obvious. Unless we were to assume that this extraordinary coincidence in the values of these two characteristic velocities, that of electromagnetic induction and that of light waves, was due to blind chance, there was no other alternative but to recognise that what we commonly called a ray of light was nothing else than a series of oscillations in the electromagnetic field, propagated from point to point. Electromagnetic waves and luminous waves were thus all one. Henceforth the two ethers, the electrical ether and the luminiferous ether, were seen to be the same continuum; electricity, magnetism and optics were merged into one single science. Now, although experimenters had attempted by various means to submit Maxwell’s views to a test, the technical difficulties were so great that no success had been achieved. It appeared clearly from Maxwell’s equations that no appreciable effects could be anticipated unless was very great; and this meant that the electric intensity would have to vary with extreme rapidity. The simplest means of obtaining a result of this kind would be to produce an oscillating field of electric intensity in which the oscillations were extraordinarily rapid, several billions a second. But no mechanical contrivance could yield such results, and apart from mechanical contrivances no other methods suggested themselves. For these reasons a number of years passed before Maxwell’s views could be put to the test.