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