ke tg ee Sada 
Puates 16-22. 
In the general introduction to the preceding portion of the work a 
concise summary of the entire system of the natural sciences was given, in 
which Physics, in a restricted sense, or Natural Philosophy, occupied a 
very important place. The following sections will be devoted to this 
science. In the above-mentioned introduction the system was traced out 
in its broadest features. Taking the general divisions there indicated, it 
will be now necessary to subdivide them, and to examine each subdivision 
with special attention. 
Natural Philosophy, or Physics, may be divided into pure and applied. 
Pure Physics will then form the theoretical portion of the science, teaching 
the laws of nature, as far as they may be inferred from careful and long 
continued observations of natural phenomena, afterwards verified and 
established by actual application to practice. Hypothesis can only be 
verified by its enabling us to develope the phenomena belonging to a certain 
class, and to predict the manner of their occurrence under certain circum- 
stances, and at certain times. In this way Newton deduced the flattening 
of the poles of the earth from the law of gravitation; Laplace calculated 
the two different diameters of the earth, and actual measurement has proved 
the truth of his results. The predictions of astronomy are founded on such 
theories ; and the actual occurrence of solar and lunar eclipses, and other 
similar phenomena, years after they had been foretold, shows the firm and 
sure ground on which these theories are based. This discovery of natural 
laws is then the object of pure physics, while the application of the laws 
thus found to surrounding nature, belongs to the department of applied 
physics. The various sections of the latter are referred to in their 
appropriate places in this work: attention will be directed for a moment to 
pure natural philosophy. 
The single branches of science seer which pure natural philosophy is 
occupied, are, 1, the theory of equilibrium of forces, or statics ; 2, the theory 
of motion, or dynamics. These two parts taken together form what is 
generally termed mechanics, properly a part of applied mathematics. 8, 
the philosophy of sound, acoustics; 4, of light, optics; 5, of heat, pyrono- 
mics ; and 6, of electricity and magnetism, which latter have in more recent 
times made astonishing progress. 
A few general observations on the peculiarities of bodies must precede 
the minute investigation of particular parts of the subject. We refer to 
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