conSIdered as fully proved, first, by the celebrated experiment of
Fizeau,* and secondly, by the ample confirmation of our own
work.t The experimental trial of the first hypothesis forms
the suhject of the present paper.
If tLe earth were a transparent body, it might perhaps be
conceded, in view of the experiments just cited, that the inter-
molecular ether was at rest in space, notwithstanding the mo-
tion of thc earth in its orbit; but we have no right to ex-
tend the conclusioll from these experiments to opaque bodies.
But there can hardly be question tilDt tbe ether can and does
pass through metals. Lorentz cites the illustration of a metallic
barometer tube. When the tube is inciined the ether in the
space above the mercury is certainly fmced out, for it is im-
compressible.:/: But again we have no right to assume that it
makes its escape with perfect freedom, and if there be any resist-
ance, however slight, we certainly could not assume an opaque
Lody such as the wbole earth to offer free passage through its
entire mass. But as Lorentz aptly remarks: "quoi qui'l en
soit, on fera bien, a mon avis, de ne pas se laisser guidel', dans
une question allssi im portante, pal' des considerations sur Ie
degre de probabilite ou de simplicite de l'une ou de I'autre
hypothese, mais de s'addresser a l'experience pour apprendre a
connaitre I'etat, de repos ou de mouvement, dans lequel se
trouve I'ether a la surface terrestl'e_"§
In April, 1881, a method was proposed and carried out for
testing the qnestion experimentally.11
In deducing the formula for the quantity to be measured,
the effect of the motion of the earth through the ether on the
path of the ray at right angles to this motion was overlooked.,