A most instructive and interesting lecture was delivered on Thursday,
the 30th January, 1913, at the Calcutta University Institute Hall, by
Dr. J. C. Bose, on the above subject. It was illustrated with
experiments and in spite of the technical nature of the subject, the
manner of treatment made the discourse extremely palatable and easy of
apprehension to the lay understanding and intelligence. The truths of
science could seldom be exposed so light-heartedly and in language
leavened with balmy humour. The lecture was very largely attended by
ladies and gentlemen, European and Indian, representing the light and
leading of the city. The chair was taken by Mr. W. R. Gourlay. Amongst
those present we noticed the Hon. Mr. Ramsay McDonald, Mr. Justice
Harington, Mr. Justice Chaudhuri, Hon'ble Mr. Gokhale, Hon'ble Mr. Lyon,
Hon'ble Mr. D. N. Sarvadhikari, Sir Gurudas Banerji, Hon'ble Mr. Apcar
and Dr. Chuni Lal Bose Rai Bahadur.
The Chairman, in a few well chosen words introduced the lecturer.
Professor Bose in going to deliver his highly interesting lecture first
showed how on account of the imperfection of our senses we fail to
detect various forces which play around us. We are not only deaf, but
practically blind. While we perceive eleven octaves of sound, we can see
only a single octave of other vibration which is called light. In order
to detect the invisible light a special detector has to be devised.
Prof. Bose showed his artificial retina previously exhibited at the
Royal Institution which not only detected luminous radiation but also
invisible lights in the intra red and ultra violet regions. In the
course of his remarks illustrating the nature of electric or Hertzian
waves, which gave rise to the invisible radiation he proceeded to
enumerate some of the conditions necessary for experimenting with them,
and to describe the apparatus he had invented for the purpose. Hertz had
used waves which were about 10 metres in length. It was impossible to
attempt any quantitative measurement of their optical properties on
account of large waves curling round corners. The lecturer had succeeded
in producing the shortest waves, with frequency of 50,000 millions of
vibrations per second, the particular invisible radiation being only
thirteen octaves below visible light. His generator produced the small
sharp beam which alone could be employed for quantitative measurements.
By means of this apparatus experiments on electric radiation could be
carried on with as much certainty as could experiments with ordinary
light. Prof. Bose then performed experiments illustrative of the
properties possessed in common by light waves and electric waves. He
exhibited the power of selective absorption to electric rays displayed
by many substances pointing out that while water stopped them, pitch,
coal tar, and others were quite transparent to them. He showed how the
rays were reflected by mirrors, obeying the same laws as light. The hand
of the experimenter was found to be a good reflector, the rays
rebounding after impact. Electric rays also undergo refraction and he
described an ingenious method he had devised by which the index of
refraction of numerous opaque substances could be obtained with the
highest exactitude. In conclusion he gave an account of his discovery of
the polarisation of electric rays by crystals. He showed that these
polarised the electric rays just as they did ordinary light. He further
proved that substances under pressure and strain could produce double
refraction in them, as did glass under the same conditions in light.
Tourmaline was useless for electric rays; but a lock of human hair was
extraordinarily efficient. According to this theoretical prediction, an
ordinary book was shown to exhibit selective absorption in a striking
manner. Thus while the Calcutta University Calendar was, usually, very
opaque, it became quite transparent when held in a particular direction
as regards the impinging ray.
Mr. Gourlay observed that the lecture opened out to himself, as well as
to other vistas, which they had never dreamt of before.
--_Amrita Bazar Patrika_, 31-1-1913.