14 



UNDULATORY FORCES. HE AT. 



[FRICTION A.KD PERCUSSION. 



horizontal, although its vortical or perpendicular position 

 will undergo continual change. 



By refining the ideas or imagination, and supposing the 

 exigence of an extremely rare substance, which has been 

 called "ether," undulations in this material have been 

 suggested as the cause of the forces of which wo have now 

 to apeak ; and, as we shall presently show, that although 

 the idea or theory has no exact foundation, still it has 

 the inestimable advantage of explaining a variety of phe- 

 I'omona for which we have no equally suitable expression. 



Taking as a postulate the existence of an ether, we 

 proceed to speak of its motion as the cause of forces ; 

 and we may here remark, that whilst the undulations oi 

 the ether may be proximate causes, we assume the ex- 

 istence of some unknown force, the action or suspension 

 of which is the ultimate cause of the proximate. Of the 

 ultimate cause we are ignorant ; we can only assign its 

 origin to the First Cause, of whom it has been recorded 



" God said, Let ihere bo light, and there was light." 



When two pebbles are cast into the same still sheet of 

 water, it will be found that the waves produced destroy 

 each other when they come in contact in certain posi- 

 tions. Transferring our attention to the undulations of 

 ether in a binary or twofold form, we can thus explain 

 the cause of interference and polarisation ; and assuming 

 that any number of undulations may be produced by a 

 similar number of initiative motions, we can, by applying 

 the doctrine, explain a vast variety of the phenomena of 

 the forces now under discussion. The reader will do 

 well to study the effects produced by casting stones into 

 still water, and by watching the results afforded when the 

 radial waves intersect each other. Indeed, we cannot 

 recommend any plan so effective for inducing an appre- 

 ciative idea of the various laws to which the undulations 

 of a fluid are subject. 



Presuming that ether has been put into motion in 

 one direction only, we can at once explain the phenomena 

 of the conduction, convection, &c., of heat; for we have 

 only to suppose motiun to have been primarily imparted, 

 and we can assume that it is propagated in every direc- 

 tion, and in every part of the body, from the centre to 

 which motion had been first applied. 



Thus, if a nail or match be struck, the percussion is 

 supposed to set ether in motion or undulation : hence 

 the production, radiation, and diffusion of heat, <fcc. If 

 we presume a double or any number of motions to have 

 been induced, we can understand that they may interfere 

 with each other, and so produce double refraction, polari- 

 sation, and analogous phenomena. 



Again, as all forces from a common centre mustdiniin- 

 ish in power, because they extend over a space equal to 

 the square of any relative distance from the central point, 

 so the undulation of an other being at once a central and 

 radial cause, will produce effects obedient to the same 

 laws. In practice, we observe that a body giving off any 

 amount of heat, will, at a distance of two feet, seem to 

 afford but one-fourth of that which is perceived at one 

 foot from it ; at three feet, the intensity of its radiant 

 heat seems to be but one-ninth, and so on. The calcula- 

 tion, therefore, of the forces of heat, light, <fec., becomes 

 one of mathematical precision ; and the laws of circles 

 and conic sections are of extreme value, and, ui fact, a 

 necessity, in wiving at accurate measurements of the in- 

 tensities of these forces, and in arranging such in a tabular 

 form. 



Having thus shown the feasible, probable, and appli- 

 cable nature of this undulatory hypothesis, we shall not 

 further enter into the subject fur the present. Under 

 the heads of Light and Acoustics, we shall have to enlarge 

 considerably on these remarks. Recapitulating our state- 

 ments, and extending them for our present purpose, we 

 presume 



1 . That Heat, Light, etc. , are produced by the undu- 

 lations of an ether. 



2. That these undulations may be propagated through 

 space, and in the pores of a body. 



3. That the rapidity of these undulations, which is 

 exceedingly great, and that their regularity in one 



direction, or their mutual interference, are the causes of 

 the intensity of the forces to which we have alluded, and 

 also of their modifications. 



Lastly. That the undulations of ether are caused by the 

 application of a force which produces the motion of its 

 parts, and consequently its phenomena. 



THE PRODUCTION OF HEAT. 



THE best known source of terrestrial heat is the sun ; but 

 the cause of its heat and light has been hitherto unas- 

 certained. By some it has been suggested that an ex- 

 tensive combustion is going on in that luminary. Recent 

 observations on the solar spots, or black patches which 

 occasionally appear on the disc, by no means countenance 

 such views ; and, indeed, it would seem that the body of 

 the sun presents the black appearance thus observed, 

 and that an external atmosphere lias the power of either 

 producing light and heat, or of, by some unexplained 

 means, inducing these effects on the earth. Future 

 researches, more especially in connexion with polarisa- 

 tion, may eventually lead to more correct views in respect 

 to the cause of the forces present in the solar rays. 



There is no doubt that the heat which all terrestrial 

 bodies afford lias been chiefly gathered from the sun: 

 and thus, although generally unobserved by the senses, 

 may be educed, by various means, to a large extent. 

 The different processes employed for the purpose we 

 shall now enumerate. They are chiefly Mechanical, 

 Chemical, and Electrical. 



FRICTION is a well-known cause of the production of 

 heat, and, in civilised and savage nations, is equally em- 

 ployed for affording flame for the ignition of fuel. 

 The common lucifer-match is well known in Europe, and 

 has succeeded the now old-fashioned flint and steel. In 

 Greenland, and in many tropical countries, the in- 

 habitants produce sufficient heat, by the friction of dry 

 wood, to ignite fuel, &c. The annexed engraving illus- 

 trates an instrument used in the arctic regions. It con- 

 sists of a straight piece of dry wood (a), into holes in 

 which the end of a small roller (6) is rapidly rubbed, in 

 much after the same style that a hole would be bored in any 

 solid ; and thus a piece of dry moss may be easily ignited. 



fig. l. 



In the operation of boring cannon, it has been found 

 that the friction evolves sufficient heat to boil water ; and 

 it has been stated, that a brass cannon, about seven-and- 

 a-half inches in diameter, will, whilst the borer makes 

 thirty revolutions in a minute, under a pressure of 

 10,000 pounds, produce sufficient heat to boil eighteen 

 pounds of water in two hours and a-half. i 



In the Exhibition of 1851, in London, an instrument 

 was used, which, by the friction of metal plates, afforded 

 sufficient heat to keep various refreshments ready for 

 use, such as coffee, (fee. ; and an arrangement has lately 

 been patented, whose object is to introduce this novel 

 mode of heating liquids into general employment. 



The axles of wheeled carriages frequently become 

 heated by their friction against their bearings. Steam 

 and spinning machinery are often seriously injured from 

 a like cause ; and many extensive fires have been pro- 

 duced through neglect in oiling their different parts. The 

 ordinary mode of grinding steel articles is an illustration 

 of light and heat being evolved by friction ; and so ex- 

 :ended is the production of heat by such means, that two 

 pieces of ice may be made to melt by being rapidly rubbed 

 against each other. 



