130 
SCIENCE. 
the age of thirteen, in the year 1804, remaining there eight years, 
and during the chief part of the time bound books. Now it was in 
those books, in the hours of the week, that I found the beginning 
of my philosophy. There were two that especially helped me, — 
the Encyclopoedia Britannica, from which I gained my first notions 
of electricity, and Mrs. Marcet's 11 Conversations on Chemistry,” 
which gave me my foundation in that science. Do not suppose that 
I was a very deep thinker, or was marked a precocious person. I 
was a burly imaginative person, and could believe in the Arabian 
Nights as easily as in the Encyclopoedia. But facts were impor- 
tant to me and saved me. I could trust a fact and always c r oss-ex- 
amined an assertion. So when I questioned Mrs. Marcet's book 
by such little experiments as I could find means to perform, and 
found it true to the facts as I could understand them, I felt that I 
had got hold of an anchor in chemical knowledge, and clung fast 
to it. Thence my deep veneration for Mrs. Marcet — first, as one 
who had conferred great personal good pleasure on me; and then 
as one able to convey the truth and principle of those boundless 
fields of knowledge which concern natural things to the young, 
untaught and inquiring mind. You may imagine my delight when 
I came to know Mrs. Marcet personally; how often have I cast my 
thoughts backward, delighting to connect the past and the present; 
how often, when sending her a paperas a thank-offVring, I thought 
of my first instructress ; and such thoughts will remain with me.” 
Henry wrote on the inside of the cover of Gregory's work the 
following words : “ This book, although by no means a profound 
work, has, under Providence, exerted a remarkable influence on my 
life. It accidentally fell into my hands when I was about sixteen 
years old, and was the first book I ever read with attention. It 
opened to me a new world of thought and enjoyment ; invested 
things before almost unnoticed with the highest interest; fixed my 
mind on the study of nature, and caused me to resolve at the time 
of reading it that I would immediately begin to devote my life to 
the acquisition of knowledge.— J. H.” Each of these philoso- 
phers worked with simple instruments, mostly constructed by his 
own hands, and by methods so direct that he appeared to have an 
almost intuitive perception into the workings of nature; and each 
gave great care to the composition of his writings, sending his dis- 
coveries into the world clothed in simple and elegant "English. 
Finally each loved science more than money, and his Creator more 
than either. There was sympa'hy between these men ; and Henry 
loved to dwell on the hours that he and Bach spent in Faraday's 
society. I shall never forget Henry's account of his visit to King's 
College, Lrndon, where Faraday, Wheatstone, Daniell and he 
had met to try and evolve the electric spark from the thermopile. 
Each in turn attempted and failed. Then came Henry's turn. He 
succeeded, calling in the aid of his discovery of the effect of a long 
interpolar wire wrapped around a piece of soft iron. Faraday be- 
came as wild as a boy, and, jumping up, shouted, “ Hurrah for the 
Yankee experiment.” And Faraday and Wheatstone reciprocated 
the high estimation in which Henry held them. During a visit to 
England, not long before Wheatstone’s death, he told me that 
Faraday and he had, after Henry's classical investigation of the 
induced currents of different orders, written a joint letter to the 
council of the Royal Society, urging that the Copley medal, " that 
laurel wreath of science," should be bestowed on Henry. On fur- 
ther consultation with members of the council it was decided to de- 
fer the honor till it would come with greater eclat, when Henry had 
continued farther his researches in electricity. Henry’s removal to 
Washington interrupted these investigations. Wheatstone prom- 
ised to give me this letter to convey to Henry as an evidence of the 
high appreciation which Faraday and he had for Henry’s genius, 
but Wheatstone’s untimely death prevented this. Both Faraday 
and he gave much thought to the philosophy of education, and in 
the main their ideas agreed. I may in this connection be excused 
from reading abstracts from a letter from Henry soon after 
he had received the news I had given my son his name. After 
a playful discusssion of the name Joseph, Jo and Josey, he says — 
what may be news to most of you : '• I did not object to Henry as a 
first name ; although I have been sorry that my grandfather, in 
coming from Scotland to this country, substituted it for Hendrie, a 
much less common, and, therefore, distinctive name.” He then 
proceeds ; “I hope that both his body and mind will be developed 
by proper training and instruction, that he may become an effic- 
ient, wise and good man. I say efficient and wise, because these 
two characteristics are not always united in the same person. In- 
deed, most of the inefficiency of the world is due to their separa- 
tion. Wisdom may know what ought to be done, but it requires 
the aid of efficiency to accomplish the desired object. I hope that 
in the education of your son due attention may not only be given 
to the proper development of both these faculties, but also they 
will be cultivated in the order of nature ; that is, doing before 
thinking; art before science. By inverting this order much injury 
is frequently done to a child, especially in the case of the only son 
of a widowed mother, in which a precocious boy becomes an insig- 
nificant man. On examination in such a case it will generally be 
found that the boy has never been drilled into expertness in the art 
of language, of arithmetic, or of spelling, of attention, persever- 
ance and order; or, in other words, of the habits of an active and 
efficient life.” 
Henry was a man of extensive reading, and often surprised his 
friends by the extent and accuracy of his information, and by the 
original manner in which he brought his knowledge before them. 
Not only was he well versed in those subjects in which one might 
naturally suppose him proficient, but in departments of knowledge 
entirely distinct from that in which he gained his reputation as an 
original thinker. Although without a musical ear he had a nice 
feeling for the movement of a poem, and was fond of drawing from 
his retentive memory poetic quotations apt to the occasion. He 
was a diligent student of mental philosophy, and also took a lively 
interest in the progress of biological science, especially in follow- 
ing the recent generalization of Darwin ; while the astonishing de- 
velopment of modern research in tracking the history of prehistoric 
man had for him a peculiar fascination. Yet with all his learning, 
reputation and influence, Henry was as modest as he was pure. 
One day. on opening Henry's copy of Young's Lectures on Natural 
Philosophy — a book which he has studied more than any other 
work of science — I read on the fly-leaf, written in his own band, 
these words : — 
” In Nature’s infinite book of secrecy 
A little I can read.” — Shakespeare. 
And did he not readalittle “in Nature's infinite book of secrecy ?” 
And did he not read that little well ? May we all read our little in 
that book as modestly and as reverently as did Joseph Henry. 
THE PHOTOPHONE. 
By Alexander Graham Bell. 
In bringing before you some discoveries made by Mr. Sumner 
Tainter and myself, which have resulted in the construction of 
apparatus for the production and reproduction of sound by means 
of light, it is necessary to explain the state of knowledge which 
formed the starting point of our experiments. I shall first describe 
the remarkable substance selenium, and the manipulations devised 
by various experiments : but the final result of our researches has 
evidenced the class of substanoes sensitive to light-vibrations, 
until we can propound the fact of such sensitiveness being a gen- 
eral property of all matter. We have found this property in gold, 
silver, platinum, iron, steel, brass, copper, zinc, lead, antimony, 
German silver, Jenkin’s metal, Babbitt’s metal, ivory, celluloid, 
gutta percha, hard rubber, soft vulcanized rubber, paper, parch- 
ment, wood, mica and silvered glass ; and the only substances 
from which we have not obtained results are carbon and thin 
microscopic glass. We find that when a vibratory beam of light 
falls upon these substances they emit sounds, — the pitch of which 
depends upon the frequency of the vibratory change in the light. 
We find farther that, when we control the form or character of the 
light-vibration on selenium, and probably on the other substances, 
we control the quality of the sound and obtain all varieties of ar- 
ticulate speech. We can thus, without a conducting wire as in 
electric telephony, speak from station to station, wherever we can 
project abeam of light. We have not had opportunity of testing 
the limit to which this photophonic influence can be extended, but 
we have spoken to and from points 213 meters apart ; and there 
seems no reason to doubt that the results will be obtained at what- 
ever distance a beam of light can be flashed from one observatory 
to another. The necessary privacy of our experiments hitherto 
has alone prevented any attempts at determining the extreme 
distance at which this new method of vocal communication will be 
available. I shall now speak of selenium. 
In the year 1817 Berzelius and Gottlieb Gahn made an examina- 
tion of the method of preparing sulphuric acid in use at Grips- 
holm. During the course of this examination they observed in 
the acid a sediment of a partly reddish, partly clear brown color, 
which, under the action of the blow-pipe gave out a peculiar odor, 
like that attributed by Klaproth to tellurium. As tellurium was a 
substance of extreme rarity, Berzelius attempted its production 
from this deposit ; bur he was unable, after many experiments, to 
obtain further indications of its presence. He found plentiful signs 
of sulphur mixed w ith mercury, copper, zinc, iron, arsenic and 
lead, but no trace of tellurium. It was not in the nature of Ber- 
zelius to be disheartened by this result. In science every failure 
advances the boundary of knowledge as well as every success, and 
Berzelius felt that, if the characteristic odor that had been observed 
did not proceed from tellurium, it might possibly indicate the pres- 
ence of some substance then unknown to the chemist. Urged on 
by this hope he returned with renewed ardor to his work. He col- 
lected a great quantity of the material, and submitted the whole 
mass to various chemical processes. He succeeded in separating 
successively the sulphur, the mercury, the copper, the tin and the 
other known substances whose presence had been indicated by his 
tests : — and after all these had been eliminated, therestill remained 
