History and Practice of the Art of Photography | Page 8

practicability of producing beautiful
solar pictures in this way; but, alas! my picture vanished and with it,
all--no not all--my hopes. With renewed determination I began again by
studying the nature of the preparation, and came to the conclusion, that
if I could destroy the part not acted upon by the light without injuring
that which was so acted upon, I could save my pictures. I then made a
strong solution of sal. soda I had in the house, and soaked my paper in
it, and then washed it off in hot water, which perfectly fixed the view
upon the paper. This paper was very poor with thick spots, more
absorbent than other parts, and consequently made dark shades in the
picture where they should not have been; but it was enough to convince
me that I had succeeded, and that at some future time, when I had the
means and a more extensive knowledge of chemistry, I could apply
myself to it again. I have done so since, at various times, with perfect
success; but in every instance laboring under adverse circumstances."
I have very recently learned, that, under the present patent laws of the
United States, every foreign patentee is required to put his invention, or
discovery, into practical use within eighteen months after taking out his
papers, or otherwise forfeit his patent. With regard to Mr. Talbot's
Calotype patent, this time has nearly, if not quite expired, and my
countrymen are now at perfect liberty to appropriate the art if they feel
disposed. From the statement of Mr. Wattles, it will be perceived that
this can be done without dishonor, as in the first instance Mr. Talbot
had no positive right to his patent.
Photography; or sun-painting is divided, according to the methods

adopted for producing pictures, into
DAGUERREOTYPE, CHROMATYPE, CALOTYPE,
ENERGIATYPE, CHRYSOTYPE, ANTHOTYPE and CYANOTYPE,
AMPHITYPE.

CHAP. II.
THE THEORY ON LIGHT.--THE PHOTOGRAPHIC PRINCIPLE
Some philosophers contend that to the existence of light alone we owe
the beautiful effects produced by the Photogenic art, while others give
sufficient reasons for doubting the correctness of the assumption. That
the results are effected by a principle associated with light and not by
the luminous principle itself, is the most probable conclusion. The
importance of a knowledge of this fact becomes most essential in
practice, as will presently be seen. To this principle Mr. Hunt gives the
name of ENERGIA.
THE NATURE of Light is not wholly known, but it is generally
believed to be matter, as in its motions it obeys the laws regulating
matter. So closely is it connected with heat and electricity that there can
be little doubt of their all being but different modifications of the same
substance. I will not, however, enter into a statement of the various
theories of Philosophers on this head, but content myself with that of
Sir Isaac Newton; who supposed rays of light to consist of minute
particles of matter, which are constantly emanating from luminous
bodies and cause vision, as odoriferous particles, proceeding from
certain bodies, cause smelling.
The effects of light upon other bodies, and how light is effected by
them, involve some of the most important principles, which if properly
understood by Daguerreotypists would enable them to improve and
correct many of the practical operations in their art. These effects we
shall exhibit in this and the following chapters. Before we enter on this
subject it will be necessary to become familiar with the
DEFINITIONS of some of the terms used in the science of optics.
Luminous bodies are of two kinds; those which shine by their own light,
and those which shine by reflected light.
Transparent bodies are such as permit rays of light to pass through
them.
Translucent bodies permit light to pass faintly, but without representing

the figure of objects seen through them.
Opaque bodies permit no light to pass through them, but reflect light.
A ray is a line of light.
A beam is a collection of parallel rays.
A pencil is a collection of converging, or diverging rays.
A medium is any space through which light passes.
Incident rays are those which fall upon the surface of a body.
Reflected rays are those which are thrown off from a body.
Parallel rays are such as proceed equally distant from each other
through their whole course.
Converging rays are such as approach and tend to unite at any one point,
as at b. fig. 3.
Diverging rays are those which continue to recede from each other, as
at e. Fig. 3.
A Focus is that point at which converging rays meet.
MOTION OF LIGHT--Rays of light are thrown off from luminous
bodies in every direction, but always in straight lines, which cross each
other at every point; but the particles of which each