On September 26, 1871, General A.J. Pleasonton, of Philadelphia, Pa.,
obtained a patent for "utilizing the natural light of the sun
transmitted through clear glass, and the blue or electric(!) solar
rays transmitted through blue, purple, or violet colored glass, or its
equivalent, in the propagation and growth of plants and animals." In
his specification, of which the above constitutes one claim, he states
that he has discovered "special and specific efficacy in the use of
this combination of the caloric rays of the sun and the electric blue
light in stimulating the glands of the body, the nervous system
generally, and the secretive organs of man and animals." He also
states that he finds that vegetation is vastly improved by the
transmitted blue light. These alleged re-discoveries--for the General
only claims to have devised the method of utilizing them--were
extensively promulgated through the press early in 1871. Subsequently,
in 1876, General Pleasonton published a book on the subject, the
volume being appropriately bound in blue and printed in blue ink.
Recently public attention has again been called to the subject by a
New York daily journal. The peculiar kind of glass in question is
known as "pot metal blue," that is, it is stained a bluish violet
throughout, and is not clear glass covered with flashings of blue
glass. It is used in greenhouses, etc., in connection with clear
glass; and in General Pleasonton's grapery it appears that only every
eighth row of panes was blue. Some of the results alleged to have been
obtained by exposing animals and plants are as follows: Twenty grape
vines, in their second year, after being set out under the blue glass,
bore 1,200 lbs. of splendid fruit. A very weak Alderney bull calf was
in four months developed into a strong and vigorous bull. Heifers when
kept under blue glass may safely bear young when 18 months old. A weak
child, weighing but 3½ lbs. at birth, weighed at the end of four
months 22 lbs.--the light in this instance having come through blue
curtains. Two major-generals with rheumatism were cured in three days.
A young lady whose hair had come out regained her tresses; and to
these must be added various other cures of severe ailments which we
have not space here to recapitulate. The above are the alleged facts;
and we propose to consider the supposed discovery in the light of
previous investigations.
With reference to the theories of electricity, etc., advanced by
General Pleasonton to account for his phenomena, their absurdity is so
complete that we shall waste no time over them. The important question
in the matter, and the only one in which the public is interested, is
whether or not blue glass is capable of producing all or any of the
results imputed to its use. In order to clear the way for the
examination of the investigations, the records of which we have
carefully collected, let us consider first those which General
Pleasonton quotes in support of his views. These are (1) Seunebier's
researches, which go to show that the blue and violet rays are the
most active in determining the decomposition of carbonic acid in
plants, and (2) experiments of Dr. Morichini, repeated by Carpa and
Ridolfi, proving that violet rays magnetized a small needle. The first
statement has been totally disproved. Dr. Von Bezold, in his recent
work on color, states that "the chemical processes in plants, as far
as they are dependent upon light, are principally caused by the rays
of medium and of lower refrangibility. The development of the green
color of the chlorophyll, the decomposition of carbonic acid, as well
as the formation of starch, etc., in the grains of the chlorophyll,
are induced by the red, green, and orange rays." The blue, violet, and
ultra violet rays, the same authority goes onto explain, influence
"the rapidity of growth, compel the so-called zoöspores to move in
certain directions, and alter the positions of leaves, etc." In
confirmation of this, we have Sach's experiments in 1872, which show
that light, transmitted through the yellow solution of potassium
chromate, enables green leaves to decompose over 88 per cent. of
carbonic acid; while that passed through blue ammonia copper oxide
decomposes less than 8 per cent. This proves the superiority of the
yellow ray to decompose carbonic acid; and this fact Professor J.W.
Draper discovered a long time ago by the direct use of the spectrum.
In still further confirmation, we may cite the investigations of
Vogel, Pfeiffer, Selim, and Placentim. The last three have conducted
researches in full knowledge of those of General Pleasonton, and their
experiments show that yellow rays are more promotive of the evolution
of carbon in animals and its absorption in plants than any others in
the spectrum, the violet rays having least power in these respects,
with the exception of the red rays in the case of animals. The
absorption of carbonic acid by plants, and its evolution by animals,
we hardly need add, are prime essentials to the growth and health of
each. The notion that light possesses a magnetizing power on steel was
upset by Niepce de St. Victor in 1861. After removing every source of
error, he "found it impossible to make one sewing needle, solarized
for a very long time under the rays of light concentrated by a strong
lens, attract another suspended by a hair, whether the light was white
or colored by being made to pass through a violet-colored glass."
We can proceed further and even show that violet light is in some
respects hurtful to plants. Cailletet, for example, says in 1868 that
"light which was passed through a solution of iodine in carbonic
disulphide prevents decomposition altogether." Baudrimont says that
"no colored light permits vegetables to go through all the phases of
their evolutions. Violet-colored light is positively injurious to
plants; they absolutely require white light." This scientist
instituted the most elaborate experiments on the subject, ranging over
11 years, from 1850 to 1861; and the result of all his labor may be
summed up in the simple statement that no illumination which human
ingenuity can devise is so well adapted for promoting natural
processes as the pure white light provided by the Creator. So much by
way of general denial of the claims of superior efficacy residing in
blue light of any kind.
Now we have yet to examine the peculiar variety of blue light here
used. Sunlight can, by means of the prism, be split into colored rays,
any one of which we may isolate, and so obtain a certain colored
light. Similarly we may obtain light of a desired color by the use of
a colored glass which will stop out the rays not of the hue required.
So that we may obtain violet light from the spectrum or by filtering
sunlight through violet glass. When, however, Dr. Von Bezold, as
above, asserts that the violet rays have such and such an effect, he
means the violet of the spectrum, which has its specific duty to
perform in the compound light of which it is a necessary portion. But
the violet light of the spectrum and filtered violet sunlight are
altogether different things. The first, as our valued contributor Dr.
Van der Weyde has very clearly pointed out, is "a homogeneous color
containing, besides the luminous, the invisible chemical rays without
any caloric rays; while the light colored by passing through violet
glass is a mixture of blue rays with the red rays at the other end of
the spectrum; and it contains a quantity of the chemical rays
belonging to the blue and the caloric rays belonging to the red. In
fact, violet glass passes a light identical with sunlight, only much
reduced in power, containing but a portion of its caloric, chemical,
and luminous agency: being simply deprived of its strongest rays." And
this the spectroscope has clearly demonstrated. Reduced to its
simplest terms, then, the necessary conclusion is that the violet
glass acts purely as a shade for decreasing the intensity of the solar
light. And in the simple fact that it does so serve as a shade lies
the sole virtue (if any there be) of the glass. In 1856, Dr. Daubeny
made experiments on the germination of seeds, and in his report is
this suggestive sentence: "In a south aspect, indeed, light which had
passed through the ammonia sulphate of copper (blue solution), and
even darkness itself, seemed more favorable than the whole of the
spectrum; but this law did not seem to extend to the case of seeds
placed in a northern aspect where the total amount of light was less
considerable."
In our next issue, we shall review the effects of light and darkness
upon the animal organization, and endeavor to account for the curing
of diseases and the production of other phenomena which have been
erroneously ascribed to the influence of the blue filtered sunlight.
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