CHAMBERS'S INFORMATION FOR THE PEOPLE. 



these to calculate the effects of all possible kinds 

 of forces, single or combined. It makes an im- 

 portant distinction between forces that are coun- 

 terbalanced so as to produce rest or equilibrium, 

 and forces productive of movement ; this gives 

 rise to two branches named Statics and Dy- 

 namics. To determine the path of a projectile 

 is a simple mechanical problem : two forces are 

 given, which, separately, would produce certain 

 known effects, and the question is to find the 

 effect of both acting together. 



Astronomy is the link between General Me- 

 chanics and Terrestrial Physics : it is a case of 

 motion and forces where the natural agent, 

 gravity, is brought into the question. Experi- 

 mental induction having traced out the law of 

 gravity as the power concerned in keeping the 

 heavenly bodies together, the principles of me- 

 chanics enable us to compute, by the help of 

 mathematics, all the consequences of this agency 

 that is, if we find that the moon is acted on 

 both by the earth and by the sun, with a certain 

 energy depending on the mass and distance of 

 each, it is possible to calculate what course she 

 will describe under the two actions, and where 

 she will be at any specified time. There are 

 certain terrestrial actions as the Tides which 

 come under Astronomy from their being caused 

 by distant gravitation. 



The first branch of Terrestrial Physics is com- 

 monly termed the Properties of Matter, meaning 

 thereby the laws and peculiarities of the aggrega- 

 tion of matter into solid, liquid, and gas. The 

 agency that succeeds to gravity is the cohesive 

 power that binds the atoms of bodies into masses 

 of more or less firmness of structure. It requires 

 us to recognise as a first principle of the composi- 

 tion of the material world, that all substances are 

 made up of exceedingly small particles or atoms, 

 which are gifted with powers of mutual attraction 

 and repulsion ; and under the action of these 

 powers become, according to the way that they 

 happen to be adjusted, solids of more or less 

 compactness, liquids, or airs. These powers of 

 adhesion are very varied and unequal, and in 

 this respect contrast with the uniformity and 

 regularity of the gravitating force. They not only 

 differ in different substances, but they differ in 

 the same substance, in consequence of there being 

 a grand pervading energy of nature, called Heat, 

 located in the first instance in the sun, which is 

 able to overrule and modify them. 



The first division of Terrestrial Physics being 

 the Laws of Material Aggregation, and the second 

 the Laws of Heat, it is usual to follow these up 

 with practical Mechanics, Hydrostatics, Pneu- 

 matics, and Acoustics which involve no new first 

 principle not contained in the previous depart- 



the polarity is most conspicuously exhibited, from 

 its acting on large masses of iron or other mag- 

 netic metal. The second of the Statical branches 

 is Frictional Electricity, or the electricity of the 

 common machine. This branch was created in 

 the latter half of last century by Franklin and 

 others. The first of the Dynamical branches is 

 termed Voltaic Electricity, or the excitement of 

 the voltaic pile, which first shewed the close con- 

 nection between electricity and chemical action. 

 Next follow Electro-magnetism and Magneto- 

 electricity, being the laws of the derivation of 

 magnetism from electricity, and conversely of 

 electricity from magnets. Thermo-electricity is 

 the derivation of the excitement from heat, which 

 completes the proof of the connection between 

 these two great natural powers. In addition to 

 all these, electricity has to be considered in its 

 relation to animal and vegetable bodies, as being 

 both produced and expended within the living 

 organism. 



The subject of Light has, in some of its bearings, 

 been set forth with great distinctness, as in all 

 the mathematical relations of its incidence, re- 

 flection, and refraction on surfaces ; but as to its 

 origin and ultimate action on the surfaces that it 

 renders visible, and on the receiving surface of 

 the eye, nothing is yet known. Most bodies, when 

 heated to some given temperature, become lu- 

 minous ; but it does not appear that any of their 

 heat is wasted in supplying the rays of light ; so 

 that, although an undoubted connection subsists 

 between light and heat, it is totally different from 

 the relation of heat to electricity. Hot bodies 

 give light in addition to their heating power ; 

 whereas, if such bodies are made to yield elec- 

 tricity, their heat is consumed or Avasted in the 

 act of being turned into electric excitement. No 

 means has yet been found of investigating the 

 changes wrought in the surfaces of bodies by the 

 action of light ; but the invention of Photography 

 seems to be a beginning in this direction. 



Chemistry is related to Physics through Heat 

 and Electricity. It treats of the circumstances 

 and laws of the combination of simples into com- 

 pounds, and the resolution of compounds into 

 simples. The combinations of chemistry take 

 place in fixed proportions, and end in producing 

 out of two substances a third so different from 

 either, that it could never be suspected to be made 

 up as it really is. 



Combination and decomposition being the great 

 facts of chemistry, it became an accurate science 

 when the laws of these processes were suggested 

 by Dalton. Chemistry is usually divided into 

 Inorganic and Organic. Organic chemistry treats 

 of the chemical composition and actions of the 

 substances that are formed in the vegetable and 



ments. There then remain the two subjects of \ animal processes. As distinguished from the 

 Electricity and Light, each involving a distinct ; materials presented by the mineral and inorganic 



natural agency. Electricity has now been com- 

 pletely generalised, and shewn to be a wide rang- 

 ing power of the polar nature, which puts on 

 many forms according to its material connections, 

 but invariably maintains the character of a polar 

 or double force. There are no less than six or 

 seven subordinate branches, falling under two 

 grand divisions,- which are distinguished by the 

 terms Statical or Reposing, and Dynamical or 

 Current Electricity. The first of the subordinate 

 branches is the oldest namely, Magnetism, where 



3C6 



world, these substances are usually very complex. 

 Sugar is by no means an extreme example of 

 organic complexity of combination ; but one of 

 its atoms contains twenty times as many atoms of 

 simples as an ordinary inorganic acid, such as 

 oil of vitriol. The products of the animal tissues 

 are far more complex than even this. The 

 number of substances in nature that are chemically 

 distinct may amount to hundreds of thousands, 

 giving thus a prodigious choice for human pur- 

 poses when once they come to be properly known. 



