SECTION I. 

 HEAT, AND ITS APPLICATIONS, 



Ix our Introductory Chapter we referred chiefly to those 

 elementary facts which may be considered as the basis of 

 Natural Philosophy. It will be necessary to recur fre- 

 quently to what may be termed the axioms of science, on 

 which we there treat ; and, presuming that a general idea 

 has been arrived at with respect to fundamental prin- 

 ciples, we proceed to consider certain forces, by whose 

 agency the external characteristics and form of all kinds 

 of matter are modified. 



To many, who are untutored in science, the heading of 

 this chapter may be suggestive of difficulty. We there- 

 fore proceed to define the term "undulatory forces." 



In producing motion by mere mechanical action such, 

 for instance, as in removing a body from its position, we 

 are conscious of exercising a force, and such is put into 

 operation by vital action. We will to do anything, and 

 action may or does follow. The sequences of cause and 

 effect are so immediate, that we do not attempt to trace 

 their relationship. 



When, however, we do not apply directly the vital 

 force, but employ others, such as heat, Arc., to produce 

 a certain result, we necessarily inquire into the inter- 

 mediate steps which exist between our will and the 

 effectuation of it* desire ; and, in this intermission, we 

 naturally seek to know what intervening causes have 

 been called to our aid. Nothing is more simple than to 

 remove a body by mere exercise of the muscles. When, 

 however, we employ an agent, as in the propulsion of a 

 ball from a cannon, we see that a variety of powers or 

 forces are called into operation ; and the object of science 

 is to ascertain their nature, and to measure their extent 

 and duration. 



The most cursory observation will show that many na- 

 tural occurrences owe their origin to a quasi -animate 

 force. If, for instance, we carefully balance two weights 

 at each end of a lever, we shall cause one to descend, or 

 to weigh down one end of the lever, if we expand that 

 end by the application of heat. An intelligent observer 

 will not be content to ascertain the facts of the case : he 

 will endeavour to find out the reason of such an effect ; 

 and to such inquiries, in reference to " Thermotics," or 

 the Science of Heat, we now direct attention. 



It has been already remarked, that a body is composed 

 of infinitely small particles, called atoms. We do not 

 know what the ultimate state of matter is. We be- 

 lieve, however, that its bulk, or the space any body 

 occupies, is solely owing to the comparative presence or 

 absence of heat or caloric. 



The question, however, arises as to the nature of a 

 force whose agency has so great an influence on natural 

 phenomena ; and to account for this, various theories 

 have been advanced. It has been supposed that heat, 

 like matter, has a solid nature ; or may be made up of 

 ultimate particles, just as matter is presumed to be. 

 To this idea there seems to be a fatal objection. For 

 if a body is what we may term solid, our experience 

 teaches that its bulk is rarely enlarged, except by the 

 introduction into its pores of another body, equal at 

 least to it in solidity. Thus, we cannot divide a piece of 

 wood by means of another piece of exactly the same 

 nature as itself, unless we use also a force equivalent 

 to overcoming the inertia of the particles of the body 

 which we propose to divide. 



Now, if we presume heat to be a material substance, 

 we must, from our practical knowledge of its nature, 

 admit, that being so subtle, it has yet escaped the evi- 

 dence of our sense* so far as solidity is concerned ; and 

 yet if it acts as matter in expanding a body, it inust 



have a force which ordinary solid matter has not. In- 

 deed, to state the case plainly, we must, assuming that 

 heat is material, at once assert that a less solid body, by 

 its own inherent power, has the ability to overcome the 

 inertia of a mass possessing a resistance greater than the 

 power which is exercised. The material theory of heat 

 may thus be reduced to an argumenium ad absurdvm; 

 and to the general reader, it may be better understood, 

 if we illustrate our position through the idea of dividing 

 a mass of gold as the solid, by a film of air as the 

 mechanical agent. 



The material theory of heat is, however, often em- 

 ployed to illustrate some of the phenomena whfch occur 

 during the abstraction from, or addition of caloric to a 

 body. We often hear at the lecture table such expres- 

 sions as "forcing or squeezing out heat;" and to the 

 philosopher, no danger arises of misconception, because 

 he uses and hears such terms as mere accommodations, 

 whose object is to popularise ideas, and to make them 

 accessible to those who have not had the advantage of 

 scientific training. Astronomers take similar liberties 

 with the facts of their science. We thus hear them speak- 

 ing of the "daily motion of the sun," <tc. ; electricians 

 speak of "currents of electricity," <tc. : all of which are 

 permissible, but, at the panic time, have a great tendency 

 to retard the progress of that rigid mental qualification 

 called truthfulness, which it would seem that Experi- 

 mental Philosophy has for the base of its operations. 



Quitting the material theory of heat, or, as it has been 

 sometimes called, the "corpuscular," because corpuscles, 

 or small particles, of this quasi-material were supposed to 

 emanate from heated bodies we now proceed to investi- 

 gate what has been termed the " undulatory theory," or 

 that which explains the production and effects of Heat, 

 Light, <tc., on the supposition that an "i-tlicr," by its 

 wave-like or undulatory motion, is their mutual cause. 



The term undulatory has been derived from the Latin 

 word unda, a wave ; and the reader will understand the 

 nature of the whole theory by performing what at first 

 sight may seem a most childish experiment ; but which 

 has, in its application, as much effect on the scientific theo- 

 ries of the present day, as had the notable one observed 

 by Newton namely, the falling of an apple. The Deity 

 impresses the same causes into His wise purposes, whether 

 that a hair shall fall from our head, or that a world shall 

 travel in its orbit the most insignificant and the grandest 

 effects alike owing their cause to the action of one uni- 

 versal law. 



On casting a pebble into a still pond, it will be observed 

 that the water forms a series of circles, all of which 

 have the point where the stone first touched the water 

 as their common centre. These waves, or undulations, 

 thus created, continue to be produced, until the edge or 

 bank of the pond prevents their further propagation. 

 At first sight it would seem that the water really moved 

 in a horizontal direction from the centre : but, on a care- 

 ful examination, such will not be found to be the case. 

 Each particle of water communicates its motion to that 

 next to it ; and thus each particle is scarcely disturbed 

 horizontally : the action rather raises the particles in an 

 upright or vertical position ; and thus the apparent and 

 actual motion afford a paradox, and also a refutation to 

 the general idea, " that seeing is believing." 



A very familiar illustration of the fact, that the body or 

 mast of the water does not move, is found in the case of a 

 ewan or other bird floating on ruffled water. Instead of 

 the bird moving in the apparent direction of the waves, 

 in the absence of tide or current, its body will retain its 



