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D. S. (David Samuel) Margoliouth.

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and quite recently a few thousand acres in England itself have been
planted with oaks for the purpose of meeting the future demands of
the navy.

The subject of the preservation of the woods is one of the highest
practical importance. Man has often acted very unwisely in the exer-
cise of his lordship of the forest, and has suffered greatly, and con-
tinues to suffer, in consequence. Great districts once populous, and
powerful as populous, have been almost converted into deserts, some
of them quite into deserts, and their people diminished in numbers
and in power, as the result of a wanton destruction of their forests.
France and other European countries have been swept by disastrous
floods, or rent by torrents rushing down their mountain-slopes, and
carrying masses of rock and gravel into the valleys and plains below,
because the forests which would have held the floods in check have
been recklessly consumed ; and now foi'est schools are established,
and all the power and wealth of governments are put forth for the
purpose of staying these evil effects, if possible, by replanting the
mountain-sides with trees, and thus restoring the protection which
Nature had originally provided. Climates have been changed for the
worse, the agricultural productiveness of countries has been lessened,
provinces have been depopulated, the health and happiness of nations
have been diminished, by the destruction of the forests ; and now sci-



THE VALUE OF OUR FORESTS. 183

ence and art and governmental authority are invoked to unite their
powers for the purpose of remedying the evil results.

We are treading the same course that other nations have trod.
Says Humboldt, " Men, in all climates, seem to bring upon future gen-
erations two calamities at once — a want of fuel and a scarcity of water."
With our comparatively sparse population and our continental stretch
of forest, it has hardly entered our minds that we could be improvi-
dent in the use of our woodlands. It has seemed to us that we had
enough, and that for ever ; and so we have consumed the forests with
a recklessness which has perhaps never been surpassed. We have even
sacrificed them by carelessness, or in the wantonness of a temporary
greed, utterly regardless of the future. Forests which have been the
growth of centuries have been swept off in a day. The lumberman
cuts the few noblest trees, or takes only the choicest portions of them
for the purposes of the arts, and burns the rest to ashes, thereby pre-
cluding another growth ujxju the spot. The miner does the same, cut-
ting off the already sparse forests, and taking no pains to replace them.
And so it is happening that our forest area, particularly in the more
recently settled portions of the country, is rapidly diminishing. The
opening of the great agricultural regions of the Ohio and the Missis-
sippi Valleys, with their superior attractiveness, has lessened the value
of much of the Eastern lands for the purpose of tillage, and, in some
portions of New England particularly, what were once corn-fields and
pastures, have been abandoned by the cultivator and a growth of trees
has come in. But as a whole our forest area has been diminishing for
a long time, and never more rapidly than within the last decade. Se-
rious evils have already come from this wasting of the woods, but
they have been spread over so wide a stretch of territory that atten-
tion has not been called to them in a way to arouse general attention
or lead to their remedy. Our streams have a diminished flow of water,
while they are marked by alternations of floods and droughts, much
greater than formerly prevailed. They are not navigable for so long
distances, nor for so large a class of boats, as they once were, nor do
they furnish so large or so uniform a supply for the mill-wheels as they
did in earlier times. Changes of climate have also resulted, affecting
the health of the people and the productiveness of the fields. These
effects have been noticed in a multitude of cases. But, in most in-
stances, they have been regarded as isolated and local occurrences,
and have not been attributed to their true cause.

In some of our Western States which are almost treeless, the bene-
ficial influence of forests has been forced upon the attention of the
people. It has been found that life may not be worth living, though
on the richest soil, if that be all. A writer of acknowledged authority,
in a lecture before the Illinois Industrial University, speaking of the
importance of trees as a shelter of crops from injurious winds, says, " I
think it may be safely estimated that an average of one twelfth part of



i84 THE POPULAR SCIENCE MONTHLY.

all our crops of grain and large fruits is destroyed by violent winds,
which such a system of protection, or its equivalent in groves, would
so far check as to prevent the destruction." Another, whose words are
quoted in the " Iowa Horticultural Report " for 1875, speaking of the
wintry storms of the Northwest, sometimes known as " blizzards," says,
" More people have been frozen within the last year in northwest Iowa
and west Minnesota than were ever murdered by the Indians in those
counties since their settlement." And he says, in regard to a remedy :
" I see none that would do but timber-planting. It alone would stop
these terrible winds, modify the climate, and furnish landmarks for
the traveler." So Professor Lacy, of the State University, in an ad-
di-ess to the Minnesota State Forestry Association, says : " The Minne-
sota State Forestry Association was organized to meet and deal with
the stern realities of facts. It was organized to meet the fact that over
more than one third of the great State of Minnesota the winds rush with
a howling fury and with a bitter cold that neither beast nor fruit-tree
can resist or withstand, and for miles not a single forest-tree rears its
head in protest. It was organized to meet the fact that, in a climate
which affords six months of winter, much of it fearfully severe, there
are thousands of farms on which there does not grow one particle of
fuel, and on which it can not be obtained without the expenditure of
both money and labor by a people often destitute of means. It was
organized to meet the fact that for miles and miles there is not a sin-
gle landmark to guide the benumbed and benighted traveler. It was
organized to meet the fact that to induce human beings to make their
houses on such farms is downright inhumanity. . . . The force of the
winds on our Western prairies can not be conceived of by you who have
always lived within the area of forests. They are simply terrible to
endure and appalling to contemplate. They carry death alike to the
unprotected beast and the more tender forms of arboreal life."

It is not surprising that people living amid such exposures of life
and property, and seeing so manifestly as they do that these are
attributable to the absence of trees, should bestir themselves in seek-
ing the appropriate remedy, that they should organize, as they have
done, forestry associations, appoint arbor-days, and engage the aid of
the State itself in offering bounties for tree-planting, and in exempt-
ing forest plantations for a time from taxation. The latter has been
done in several of the Western States, and already the work of tree-
planting has wrought a perceptible change on many a farm, as to
appearance, comfort of living, and productiveness. But the work
that is needed is a great one, a work not to be accomplished by plant-
ing in a few States or portions of States lines of quick-growing, soft-
wooded trees, which may make tolerable wind-breaks in five or six
years. This is hardly more than a makeshift at the best. The work
is broader and more comprehensive than that, and one which for its
due accomplishment needs an intelligent comprehension of the fact;^



THE VALUE OF OUR FORESTS. 185

involved in the ease, and tlieir far-reaching relations. It is a matter
not of present or local exigency merely, but of general and abiding
importance. The future of the whole country is involved in it.

Champollion is reported as saying in reference to the great desert
of Northern Africa : " And so the astonishing truth dawns upon us
that this desert may once have been a region of groves and fountains,
and the abode of happy millions. Is there any crime against Nature
which draws down a more terrible curse than that of stripping Mother
Earth of her sylvan covering ? The hand of man has produced this
desert, and, I verily believe, every other desert upon the surface of this
earth. Earth was Eden once, and our misery is the punishment of
our sins against the world of plants. The burning sun of the desert
is the angel with the flaming sword who stands between us and para-
dise."

An awakening of general interest on this subject is needed. To this
end the most important step is to get before the people as widely as
possible the facts showing the importance of the forests in their rela-
tions to climate, to water-supply, to floods and droughts, to commerce
and manufactures, to agriculture and to health ; the rapidity with
which we are destroying our forests and bringing upon ourselves the
natural and inevitable results of that course. The history of other
nations, as related to their treatment of the forests, should be made
widely known, and the danger that this land, or portions of it, by the
reckless destruction of its forests, may be converted into a desert, as
other lands have been. Thus may we hope to arouse a general inter-
est in the trees, and a disposition to cherish them as our best friends.
Meanwhile, let tree-planting be encouraged. Let it be shown, as it
has been again and again, that much of our poor and what is com-
monly regarded as waste land can be made to yield a handsome profit
by being devoted to the growth of trees ; and that our rough hills and
mountain-sides can thus be made of direct pecuniary value, while at
the same time they are rendered objects of beauty and the means of
protecting our springs, maintaining the flow of our streams, and pro-
moting health and prosperity. With this awakened interest in the
forests, sylviculture will come to be one of our arts. We want an
intelligent and scientific observation of the facts in regard to trees as
related to our various soils and situations. The adaptation of trees to
one climate or another, their comparative value for one purpose or
another, the obstacles to successful planting — these, and many other
things, need to be known as they are not yet known. Some things Ave
can learn from the experiments which have been made and the knowl-
edge which has been gained in Europe. But so different are the trees
there and here, and so different the conditions of soil and climate,
that the problem set before us is virtually a new one, which must be
worked out carefully and patiently on our own ground. The most
important advance in this direction yet made here, so far as we know,



i86 THE POPULAR SCIENCE MONTHLY.

lias been by the Bussey Institute, in connectiion with the Arnold
Arboretum, at Brookline, Massachusetts, Under the able and judi-
cious management of Professor Sargent, it has already fine plantations
of forest-trees, has diffused much valuable information in regard to the
growth and importance of trees, and has secured the planting of a
large number in various parts of the country. On the foundation of
such institutions will naturally be built up in due time schools of
instruction in forestry like those of Europe, which will have a recog-
nized and permanent place among us. The European schools of for-
estry will form the subject of another article.



PRODUCTIOX OF SOUND BY RADIANT ENERGY.*

Bv ALEXANDER GKAIIAM BELL.

IN a paper read before the American Association for the Advance-
ment of Science, last August, I described certain experiments made
by Mr. Sumner Tainter and myself which had resulted in the construc-
tion of a " Photophone,''^ or apparatus for the production of sound by
light ; t and it will be my object to-day to describe the progress we
liave made in the investigation of photophonic phenomena since the
date of this communication.

In my Boston paper the discovery was announced that thin disks
of very many different substances emitted sou7ids when exposed to the
action of a rapidly-interrupted beam of sunlight. The great variety
of material used in these experiments led me to believe that sonorous-
ness under such circumstances would be found to be a general property
of all matter.

At that time we had failed to obtain audible effects from masses of
the various substances which became sonorous in the condition of thin
diaphragms, but this failure was explained upon the supposition that
the molecular disturbance produced by the light was chiefly a surface
action, and that under the circumstances of the experiments the vibra-
tion had to be transmitted through the mass of the substance in order
to affect the ear. It was therefore supposed that, if we could lead to
the ear air that was directly in contact with the illuminated surface,
louder sounds might be obtained, and solid masses be found to be as
sonorous as thin diaphragms. The first experiments made to verify

*A paper read before the National Academy of Arts and Sciences, April 21, 1881.
(From author's advance-sheets.)

t " Proceedings of American Association for the Advancement of Science," August 27,
1880 ; see, also, "American Journal of Science," vol. xx, p. 305 ; " Journal of the American
Electrical Society," vol. iii, p. 3 ; " Journal of the Society of Telegraph Engineers and
Electricians," vol. ix, p. 404 ; " Annales dc Chimie et de Physique," vol. xxi.



PRODUCTION OF SOUND BY RADIANT ENERGY. 187

this hypothesis pointed toward success. A beam of suidight was
focused into one end of an open tube, the ear being placed at the
other end. Upon interrupting the beam, a clear, musical tone was
heard, the pitch of which depended upon the frequency of the interrup-
tion of the light and the loudness upon the material composing the tube.

At this stage our experiments were interrupted, as circumstances
called me to Europe.

While in Paris a new form of the experiment occurred to my mind,
which would not only enable us to investigate the sounds produced by
masses, but would also permit us to test the more general proposition
that sonorousness, under the influence of intennitte7it light, is a projj-
erty common to all lAatter.

The substance to be tested was to be placed in the interior of a
transparent vessel, made of some material which (like glass) is trans-
parent to light, but practically opaque to sound.

Under such circumstances the light could get in, but the sound
produced by the vibration of the substance could not get out. The
audible effects could be studied by placing the ear in communication
with the interior of the vessel by means of a hearing-tube.

Some preliminary experiments were made in Paris to test this idea,
and the results were so promising that they were communicated to the
French Academy on October 11, 1880, in a note read for me by M.
Antoine Breguet.* Shortly afterward I wrote to Mr. Tainter, sug-
gesting that he should carry on the investigation in America, as cir-
cumstances prevented me from doing so myself in Europe. As these
experiments seem to have formed the common starting-point for a
series of independent researches of the most important character, car-
ried on simultaneously, in America by Mr. Tainter, and in Europe by
M. Mercadier,f Professor T)Tidall,J "\V. E. Rontgen,* and W. H.
Preece,|| I may be permitted to quote from my letter to Mr. Tainter
the passage describing the experiments referred to :

Metropolitan Hotel, Rce Cambon, Paris, November 2, 1880.

Dear Mr. TAixyEK : . . . I have devised a method of producing sounds by
the action of an intermittent beam of light from substances tliat can not be ob-
tained in the shape of thin diaphragms or in the tubular form ; indeed, the meth-
od is specially adapted to testing the generality of the phenomenon we have dis-
fovered, as it can be adapted to solids, liquids, and gases.

Place the substance to be experimented with in a glass test-tube, connect a

* " Comptes Rendus," vol. cxl, p. 595.

+ " Notes on Kadiophony " (" Comptes Rendus," December 6 and 13, 1S80 ; February
_; and 28, 1881). See, also, " Journal de Physique," vol. x, p. 53.

X " j\.ction of an Intermittent Beam of Radiant Heat upon Gaseous Matter " (" Pro-
ceedings of the Royal Society," January 13, 1881, vol. xxsi, p. 307).

^ " On the Tones whiclv arise from the Intermittent Illumination of a Gas." (See
"Annalen der Physik und Cheinie," January, 1881, No. 1, p. 155.)

I " On the Conversion of Radiant Energy into Sonorous Vibration " (" Proceedings
of the Royal Society," March 10, 1881, vol. xxxi, p. 506).



188 THE POPULAR SCIENCE MONTHLY.

rubber tube with the mouth of the test-tube, placing the other end of the pipe
to the ear. Then focus the intermittent beam upon the substance in the tube. I
have tried a large number of substances in this way with great success, although
it is extremely difficult to get a glimpse of the sun here, and when it does shine
the intensity of the light is not to be compared with that to be obtained in Wash-
ington. I got splendid effects from crystals of bichromate of potash, crystals of
sulphate of copper, and from tobacco-smoke. A whole cigar placed in the test-
tube produced a very loud sound. I could not hear anything from plain water,
but when the water was discolored with ink a feeble sound was heard. I would
suggest that you might repeat these experiments and extend the results. . . .

Upon ray return to Washington in the early part of January,* Mr.
Tainter communicated to me the results of the experiments he had
made in my laboratory during my absence in Europe.

lie had commenced by examining the sonorous properties of a vast
number of substances inclosed in test-tubes in a simple empirical search
for loud effects. He was thus led gradually to the discovery that cot-
ton-wool, worsted, silk, and fibrous materials generally, produced much
louder sounds than hard, rigid bodies like crystals, or diaphragms sucli
as we had hitherto used.

In order to study the effects under better circumstances, he inclosed
his materials in a conical cavity in a piece of brass closed by a flat
plate of glass, A brass tube leading into the cavity served for con-
nection with the hearing-tube. When this conical cavity was stuffed
with worsted or other fibrous materials the sounds produced were much
louder than when a test-tube was employed. This form of receiver is
shown in Fig. 1.

Fig. 1.




Mr. Tainter next collected silks and worsteds of different colors,
and speedily found that the darkest shades produced the best effects.
Black worsted especially gave an extremely loud sound.

As white cotton-wool had proved itself equal, if not superior, to
any other white fibrous material before tried, he was anxious to obtain
colored specimens for comparison. Not having any at hand, however,
he tried the effect of darkening some cotton-wool with lampblack.

* On the Vth of January.



PRODUCTION OF SOUND BY RADIANT ENERGY. 189

Such a marked reenforceraent of the sound resulted that he was in-
duced to try lampblack alone.

About a teaspoonful of lampblack was placed in a test-tube and
exposed to an intermittent beam of sunlight. The sound produced
was much louder than any heard before.

Upon smoking a piece of plate-glass, and holding it in the inter-
mittent beam with the lampblack surface toward the sun, the sound
produced was loud enough to be heard, with attention, in any part of
the room. With the lampblack surface turned from the sun, the sound
was much feebler.

Mr. Tainter repeated these experiments for me immediately upon
my return to Washington, so that I might verify his results.

Upon smoking the interior of the conical cavity shown in Fig. 1,
and then exposing it to the intermittent beam, with the glass lid in
position as shown, the effect was perfectly startling. The sound was
so loud as to be actually painful to an ear placed closely against the
end of the hearing-tube.

The sounds, however, were sensibly louder when we placed some
smoked wire-gauze in the receiver, as illustrated in the drawing (Fig. 1).

When the beam was thro"WTi into a resonator, the interior of which
had been smoked over a lamp, most curious alternations of sound and
silence were obsei-ved. The interrupting disk was set rotating at a
high rate of speed, and was then allowed to come gradually to rest.
An extremely feeble musical tone was at first heard, which gradually
fell in pitch as the rate of interruption grew less. The loudness of the
sound produced varied in the most interesting manner. Minor reen-
forcements were constantly occurring, which became more and more
marked as the true pitch of the resonator was neared. When at last
the frequency of interruption corresponded to the frequency of the
fundamental of the resonatof, the sound produced was so loud that it
might have been heard by an audience of hundreds of people.

The effects produced by lampblack seemed to me to be very ex-
traordinary, especially as I had a distinct recollection of experiments
made in the summer of 1880 with smoked diaphragms, in which no such
reenforcement was noticed.

Upon examining the records of our past photophonic experiments
we found in vol. vii, p. 57, the following note :

Experiment Y. — Mica diaphragm covered with lampblack on side exposed to
light.

liesult : distinct sound about same as without lampblack. — A. G. B., Juhj
18, 1880.

Verified the above, but think it somewhat louder than when used without
lampblack.— S. T., July 18, 1880.

Upon repeating this old experiment we arrived at the same result
as that noted. Little if any augmentation of sound resulted from



190



THE POPULAR SCIENCE MONTHLY.



smoking the mica. In this experiment the effect was observed by
placing the mica diaphragm against the ear, and also by listening
through a hearing-tube, one end of which was closed by the dia-
phragm. The sound was found
to be more audible through the
f x'ee air when the ear was placed
as near to the lampblack sur-
face as it could be brought
without shading it.

At the time of my commu-
nication to the American Asso-
ciation I had been unable to
satisfy myself that the sub-
stances which had become so-
norous under the direct influ-
ence of intermittent sunlight
were capable of reproducing
the sounds of articulate speech
imder the action of an undu-
latory beam from our photo-
phonic transmitter. The dif-
ficulty in ascertaining this will
be understood by considering
that the sounds emitted by
thin diaphragms and tubes
were so feeble that it was im-
practicable to produce audible
effects from substances in these
conditions at any considerable
distance away from the trans-
mitter ; but it was equally im-
possible to judge of the effects
produced by our articulate
transmitter at a short distance
away, because the speaker's
voice was directly audible
through the air. The extreme-
ly loud sounds produced from
lampblack have enabled us to
demonstrate the feasibility of
using this substance in an ar-
ticulating photophone in place
of the electrical receiver for-
merly employed.

The drawing (Fig. 2) illus-
trates the mode in which the ex-




PRODUCTION OF SOUND BY RADIANT ENERGY. 191



periment was conducted. The diaphragm of the transmitter (A) was
only five centimetres in diameter, the diameter of the receiver (B) was





also five centimetres, and the dis-
tance between the two was forty
metres, or eight hundred times the
diameter of the transmitting dia-
phragm. We were unable to ex-
periment at greater distances with-
out a heliostat, on account of the
difticulty of keeping the light
steadily directed on the receiver.
Words and sentences spoken into
the transmitter in a low tone of
voice were audibly reproduced by
the lampblack receiver.

In Fig. 3 is shown a mode of in-
terrupting a beam of sunlight for
producing distant effects without
the use of lenses. Two similarly-
perforated disks are employed, one
of which is set in rapid rotation,
while the other remains stationary.
This form of interrupter is also
admirably adapted for work with
artificial light. The receiver illus-
trated in the drawing consists of a
parabolic reflector, in the focus of
which is placed a glass vessel (A)
containing lampblack or other sen-
sitive substance, and connected with



192 THE POPULAR SCIENCE MONTHLY.



Online LibraryD. S. (David Samuel) MargoliouthThe Popular science monthly (Volume 19) → online text (page 24 of 110)