40 



UNDULATORY FORCES. HEAT. 



[CONCLUDING REMARKS. 



the forces of nature. We have found, that whether calo- 

 ric be considered either as a material substance, or as 

 resulting from the vibrations of an ether, it has certain 

 definite effects on matter. These, whilst characteristic 

 of tho action of an individual force, are yet analogous to 

 those of light, as we shall see in our next section. 



We preferred to call the attention of the student to 

 caloric, as the first in our arrangement of the undulatory 

 forces ; because the principles we have enunciated, call 

 for less mental exertion to comprehend, than those of 

 the forces which we have now to consider. We must, 

 however, presume, that what we have already stated 

 has been fully understood ; and that we shall only have 

 to refer incidentally, in future, to those laws we have 

 attempted to unfold. This will be necessary, as tending 

 to save space, time, and useless repetitions. 



It may, however, be desirable, that we should point 

 out those special analogies which exist between the laws 

 of heat and light, to which we shall have to give promi- 

 nence in our future progress. To this end, the student 

 should pay particular attention to the facts connected 

 with the production, conduction, radiation, absorption, 

 reflection, refraction, and polarisation of caloric ; because 

 we must go over exactly the same ground under the 

 sections of Light and Sound, and show the nature of those 

 phases of force under similar but non-identical circum- 

 stances. It is also advisable that a clear knowledge of 

 the doctrine of undulations should have been acquired ; 

 and this is more easily arrived at whilst studying the 

 effects of heat, than those of other forces ; because such 

 are highly palpable to the senses, and familiar to us in 

 the occurrences of daily life. 



In conducting the experiments which we shall adduce 

 in the next section, in support of the principles of opti- 

 cal science, much delicacy of manipulation is frequently 

 required. This, we are aware, is not to be obtained ex- 

 cept by long practice. Still, the experiments we have 

 already offered, will serve as an introduction to those 

 which follow ; and a frequent repetition of the past, will 

 much assist our progress in the future. Clever experi- 

 menters often achieve more success in the study of 

 natural philosophy than deep thinkers ; and the latter 

 class often owe the greater part of the success which 

 attends their speculations, to the ready and accurate 

 manipulation of their more expert, but not less valuable, 

 co-workers in the pursuit of scientific research. 



There are remote analogies existing between the 

 latency of heat and light, so far as their separate or 

 mutual production from matter, by mechanical or other 

 agency, is concerned. The student will find examples of 

 this in our remarks and experiments on the production 

 of heat ;* a re-perusal of which may assist hiin materially 

 in understanding similar phenomena, belonging more ex- 

 clusively to luminous effects. 



Sec anlt, pp. 14 and 51. 



Under the head of double refraction and the polarisa- 

 tion of light, we shall have an opportunity of consider- 

 ably enlarging on similar effects to which caloric is sub- 

 ject ; to which allusion has already been made.f In the 

 course of the work, we shall continually make the re- 

 marks in one section to relate to those of the preceding 

 one ; conceiving that such a course has the twofold ad- 

 vantage, of impressing the truths of science on tho 

 minds of our readers, and also of maintaining that 

 intimate and interesting connection which exists in every 

 department of experimental philosophy. 



The subject of Terrestrial Heat is of great interest, in 

 relation to that of Physical Geography and Geology ; to 

 each of which we shall hereafter devote an entire section. 

 Dr. Tyndall's discoveries a resume of which precedes 

 these remarks may be studied advantageously in con- 

 nection with it ; and if our readers should wish to 

 pursue the subject more fully, we would recommend tho 

 perusal of Captain Maury's late work, The Physical 

 Geography of the /Sea; from which we have made a 

 quotation.! 



Those who may be desirous of turning our remarks 

 on Ventilation, Warming, <tc. , to practical purposes, 

 will find these subjects ably discussed in works by Dr. 

 Arnott, Mr. Hood, Mr. Tomlinson, and others. We 

 have only attempted to explain general principles, and 

 their immediate application, because our limits would 

 not permit of lengthened details : we, however, hope that 

 the suggestions and observations we have made, will 

 tend to excite the interest of many, who may have both 

 the means and opportunity of applying them to the 

 physical advantage of their less favoured dependents 

 and neighbours. We may especially urge such consi- 

 derations on individuals connected with establishments 

 wherein large numbers of persons are congregated, such 

 as hospitals, workhouses, schools, &c. 



To many, it would seem desirable that we should 

 have included a popular description of the steam-engine ; 

 but as we intend, in another part of this work, to de- 

 vote a section to that interesting subject, any further 

 exposition of its construction, <tc. , would have been out 

 of place. We shall also have to extend our remarks on 

 the laws of vapour and gases, when treating on Pneu- 

 matics. The various forms of land, marine, and loco- 

 motive engines, will naturally fall to be considered 

 under the head of Mechanical Philosophy. 



Having thus endeavoured to assist the student in 

 carrying out a connected system of self-instruction, we 

 proceed, in the next section, to discuss the doctrines of 

 Optical Science, or that branch of philosophical inquiry 

 in which the nature, laws, and applications of Light are 

 investigated. We shall also deal with the construction 

 and management of Optical Instruments, Photography, 

 and other allied subjects. 



t Ante, p. 28, ft ley. 



t Ante, p. 57 



