objection, in another form, is that the image is more or less indistinct.
This is answered by a glance at the tables. These show that in each
individual observation the average error was only three ten-thousandths of
the whole deflection.



Uncertainty of Laws of Reflection and Refraction in Media in Rapid
Rotation.


What is probably hinted at under the above heading is that there may be a
possibility that the rapid rotation of the mirror throws the reflected
pencil in the direction of rotation. Granting that this is the case, an
inspection of Fig. 14 shows that the deflection will not be affected.

In this figure let _m m_ be the position of the mirror when the light
first falls on it from the slit at _a_, and _m′ m′_ the position when the
light returns.

[Illustration: FIG. 14.]

From the axis _o_ draw _op op_, perpendicular to _m m_ and to _m′ m′_,
respectively. Then, supposing there is no such effect, the course of the
axis of the pencil of light would be _a o c_ mirror _c o a′_. That is, the
angle of deflection would be _a o a′_, double the angle _p o p′_. If now
the mirror be supposed to carry the pencil with it, let _o c′_ be the
direction of the pencil on leaving the mirror _m m_; i.e., the motion of
the mirror has changed the direction of the reflected ray through the
angle _c o c′_. The course would then be _a o c_, mirror _c′ o_. From _o_