Everett in his last edition of ' Units and Physical Constants.' Prof. Fitzgerald has pointed out (Phil. Mag. April 1889) that if a system be taken " in which the dimensions of B and k are the same, and of the dimensions of a slowness, that is the inverse of a velocity (L-IT), then the two systems become identical as regards dimensions, and differ only by a numerical coefficient just as centimetres and kilometres do." But although p and k are quantities of the same order, both being capacities,

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... heir dimensions need not necessarily be the same, unless electrification and magnetization be phenomena of the [pk] = (rap)*, * See dso " On the Dimensions of a Magnetic Pole in the Electrostatic Syrtem of Units," Dr. Lodge, Phil. Mag. Nov. 1882. OF PHYSICAL QUANTITIES TO DIRECTIONS IN SPACE. 359 same order as well. If, however, these be different ordersas they almost certainly are-the one possibly a strain, the other a vortex motion, then it is unlikely that k and p, bearing, as each does, similar relations to two dissimilar phenomena, should have identical dimensions. -.