rays are reflected from plane and curved mirrors in the same way and
subject to the same laws. Electric rays, like rays of light are
refracted. Like race of light too, electric waves can be selectively
stopped by various substances, which are "electrically" coloured. Water
which is a conductor of electricity stops the electric ray; where as
liquid air which is a non-conductor is quite transparent to the rays.

Finally Professor Bose explained his discovery of Polarisation of these
rays by various crystals. Tourmaline, which was a good polariser for
ordinary light, was not so effective. The lecturer discovered that the
crystal Nemalite possessed the power of polarising the electric rays in
the most perfect manner. Professor Bose also explained how the internal
constitution of an opaque mass was revealed by the help of light which
was itself invisible.

The lecturer concluded his discourse by drawing attention to the
limitations of human perception. Man's power of hearing was confirmed to
eleven octaves of sound notes. In the case of vision the limitation was
far more serious, his power of sight extending only through a single
octave of those ether waves which constituted light. These ether
vibrations of various frequencies could be maintained by electrical
means. By pressing the stop button of the apparatus which was exhibited,
ether vibrations, 50,000 millions per second, were produced. A second
stop gave rise to a different vibration. Let his audience imagine a
large electric organ provided with an infinite number of stops, each
stop giving rise to a particular ether note. Let the lowest stop produce
one vibration a second. They should then get a gigantic wave of 186,000
miles long. Let the next stop give rise to two vibrations in a second,
and let each succeeding stop produce higher and higher notes. Let them
imagine an unseen hand pressing the different stops in rapid succession,
producing higher and higher notes. The ether note would thus rise in
frequency from one vibration in a second, to tens, to hundreds, to
thousands, to hundreds of thousands, to millions, to millions of
millions! While the ethereal sea in which they were all immersed were
being thus agitated by these multitudinous waves, they would remain
entirely unaffected, for they possessed no organs of perception, to
respond to these waves.

As the ether note rose still higher in pitch, they would for a brief
moment perceive a sensation of warmth. This