X. DEPARTMENT: 



ACROPHYSICS. 



IN the department of Acrophysics, we include those branches of 

 science which relate to the dynamical laws of matter, or the agencies 

 by which the inanimate material world is regulated. The name is 

 derived from the Greek, axpo$, high, and <j>v<jt$, nature ; properly sig- 

 nifying the higher study of nature ; that is, as regards material objects. 

 The term Physics, has been variously applied ; sometimes limited to 

 the mathematical, and at others extended to the chemical laws of 

 matter ; sometimes including both Natural Philosophy and Natural 

 History, but more frequently confined to the former. Hence the 

 desirableness of a generic term, which, being strictly defined, may 

 designate exclusively the class of sciences constituting the present 

 department. The term Natural Philosophy, might suffice for this 

 purpose, were it not liable to ambiguity : but it sometimes excludes 

 Astronomy ; and is generally considered as exclusive of Chemistry ; 

 although we have high authority for regarding this latter branch as a 

 part of the same group of sciences. 



In the department of Acrophysics, we therefore place not only Me- 

 chanics, Optics, Electricity, and Calorics, which are usually com- 

 prehended under Natural Philosophy; but also the branches of 

 Astronomy and Chemistry ; as chiefly relating to the general laws, 

 though partly to the special productions of nature. Most of these 

 sciences depend more or less on the pure mathematics for their elu- 

 cidation; and hence were formerly, and are still occasionally designa- 

 ted as Mixed Mathematics. But the data, or facts, to which the 

 calculations are applied, we obtain chiefly from observation and ex- 

 periment : hence these branches have also been comprehended under 

 the name of Experimental Philosophy ; though this term is most 

 frequently applied to the studies of Optics, Electrics, and Calorics. 

 The uses to which this department of science may be applied, are 

 numerous and important; not only in dispelling superstition, and 

 elevating the mind, by explaining the wonderful phenomena and 

 operations of nature ; but in aiding the physical arts, by a knowledge 

 of the facts which they require, for their successful practice, and 

 farther improvement. 



By the general term, matter, is meant any substance which is 

 capable of affecting our senses. Matter exists in three states ; solid, 

 liquid, and gaseous. In the first, the particles cohere together, so 

 as not to be freely separated ; in the second, they cohere slightly, but 

 separate freely ; and in the third, or aeriform state, they not only 

 separate freely, but tend to recede from each other, as far as the 

 space which they occupy, or pressure which they experience, will 

 allow. Liquids and gases are both termed fluids ; the former in- 



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