y two other colors. As an example of such a
formation, a ray of white light was passed separately through a solution of
yellow chromate of potash and an alkaline litmus solution, throwing
respectively a yellow and violet-blue color upon the screen. When the ray
was made to pass through the two solutions successively, an orange-yellow
color was obtained upon the screen, which color Lord Rayleigh asserted to
be made up of red and green rays. To prove this, the ray of white light was
decomposed by means of a prism, and the decomposed rays passed through the
two solutions. The one solution was found to exclude all the yellow and
orange rays from the spectrum, while the other excluded all the blue and
violet rays, so that when the ray had passed through both solutions, only
the red and green rays were left. If, instead of allowing the decomposed
ray of light to pass through a slit, and thus obtain definite bands in the
spectrum, the ray was passed through a circular hole, the red and green
colors overlapped each other on the screen, forming by their combination
the identical orange-yellow color obtained with the primary white light. It
was then stated that if three definite positions be taken in a spectrum in
the red, green, and violet bands respectively, and these positions be
represented by the corners of an equilateral triangle (Clerk Maxwell's
triangle), it has been mathematically determined in what position within
this triangle the colors of Newton's rings would fall. Lord Rayleigh, by
means of a diagram and the selenite wedge, showed that the relations to the
three standard colors in practice were identical with the position assigned
them by theory.

In conclusion, the lecturer showed a piece of glass, the surface of which
had been decomposed, a ray of light transmitted through which showed upon
the screen patches of very pure color. These he considered to be due to the
glass consisting of a number of thin plates, some of which had been removed
by the decomposition.

* * * * *

BELT JOINTS.

From time to time, serious accidents have taken place, and the progress of
work stopped, by the sudden snapping of driving belts in machinery, and, as
a general rule, it is found that the collapse is attributable either to
faulty leather or insecure joining. A great improvement of the leather
intended for belts has been brought about during the last few years, by the
introduction of improve