No. XXIII.] APPENDIX. 323 



transferred to any other body : by conduction, that is, through bodies in 

 contact ; or by radiation, that is, to bodies at a distance. In every case 

 where heat ceases, either the new attraction ceases to exert itself, or the 

 former attraction is destroyed, and disintegration, decomposition, or motion 

 is the result. 



Some difficulty is presented to our knowledge of the actions and re- 

 actions which constitute heat, but, upon the whole, I am inclined to 

 think that heat is best described as that action of matter which from 

 a distance influences the nerves of sensation in the skin, or, in other 

 words, heat is that which is felt from a distance by the skin. 



There is another range of actions and reactions which are not 

 appreciated by the skin, but are alone seen by the eye. This range is 

 termed light, and by the prism we are enabled at once to distinguish that 

 which is seen by the eye, or light, from that which is not seen by the eye. 

 Chemistry indicates that there are actions both more refrangible than the 

 violet ray on the one hand, and less refrangible than the red on the other. 

 For the production of light the new attractions must be of the most 

 powerful kind, so that they may act with great intensity upon matter 

 attracted, and it is preferable to be in a solid state. The inflammation 

 of hydrogen gives little or no light : add solid matter, and a beautiful 

 light is the result. Hydro-carbons give us the most convenient light 

 when they are burnt with such energy that the solid matter is first 

 deposited to be acted upon by the new attraction, and subsequently burnt 

 that it may yield no smoke ; if all is burnt at once, so that no solid matter 

 remains in the flame, light will not be produced. An illuminated body may 

 communicate the force which is seeking to act upon the solid matter to 

 other bodies, and finally decomposition, disintegration, or some destruction 

 of attraction takes place. 



As the skin feels heat, the eye sees light ; so, by the ear, are we made 

 acquainted with the actions and reactions constituting sound. The 

 vibrations constituting sound have been accurately measured by philo- 

 sophers ; and though different people differ in the power of appreciating 

 the higher and lower notes, it may be generally stated that all vibrations 

 from 8 in a second to 24,000 are appreciated by the ear, and are conse- 

 quently sound. 



Sound, like light and heat, requires attracted matter : this is acted 

 upon by a new attraction, and in the conflict between the old and new 

 attractions vibrations ensue ; whilst the vibration continues, the force may 

 be propagated to other matter which may also take on vibrations. 



I have always thought that odours constituted a further range of 

 actions and reactions. I am the more confirmed in that view, the more 

 I watch those animals, as the bloodhound, which have the nerves of the 

 nose highly developed. Upon this matter, however, we are much in the 

 same position as the man born blind, who can only receive his ideas of 

 light through the medium of the eyes of others, for man has literally only 

 a rudimentary nose, if it be compared with that of other animals. 



A theory is not to be a mere mental creation, but a law or principle to 

 guide our actions and bring forth fruit. The law which I have developed 

 is so pre-eminently of practical application, that every human action may 

 be regulated by it. When we desire to obtain any result, we begin by 

 generating new attractions. For this purpose we select substances having 



Y 2 



