The conclusion of my second Philosophical Transactions paper—that of 1897—is that neither an electric nor a magnetic transverse field confers viscosity upon the ether, nor enables moving matter to grip and move it rotationally.
Question of a Possible Longitudinal
Magnetic Drift.
Later I tried a longitudinal magnetic field also; arranging a series of four large electric bobbins or long coils along the sides of a square inscribed at 45° in the optical square, Figs. [11] and [13]; so that the light went along their axes.
The details of this experiment have been only partially recorded, but the salient points are to be found stated in the Philosophical Magazine for April, 1907, pages 495-500.
The result was again negative; that is to say, a magnetic field causes no perceptible acceleration in a beam of light sent along the lines of force. The extra velocity that could have been observed would have been 1/9th of a millimetre per second, or 16 miles per hour, for each C.G.S. unit of field intensity.
Another mode of expressing the result is that the difference of magnetic potential applied, namely, a drop of two million C.G.S. units of magnetic potential, does not hurry light along it by so much as 1/50th part of a wave-length.
There may be reasons for supposing that some much slower drift or conveyance than this is really caused in the ether by a magnetic field; but if so, the ether must be regarded as so excessively dense that the amount of such a drift for any practicable magnetic field seems almost hopelessly beyond experimental means of detection.