APPENDIX 153 



To convert centigrade into Fahrenheit multiply by 9, 

 divide by 5, and add 32. 



Example: 36 x 9 = 324. 324 -s- 5 = 64.8. 64.8 + 32 = 96.8 F. 



Heat is transmitted by conduction, radiation, and 

 convection. Hold a poker in the fire until the end is 

 red hot and you will find the part in the hand uncom- 

 fortably warm. This is heat transmitted by conduction, 

 Place water in a vessel and apply heat to the bottom. 

 The heated particles of water rise to the top. This is 

 transmitting by convection. When sitting before an open 

 fire one often places a screen between the fire and one's 

 person to prevent the radiation of the heat rays. If the 

 air were heated uniformly by the fire the screen would be 

 no protection. This is radiation of heat. 



Heat is employed to liquefy solids (fusion), to alter 

 organic bodies as in roasting, to separate volatile from 

 less volatile matter (vaporization), to destroy organic 

 life as in sterilization and, particularly by the chemist, 

 in many other processes. 



LIGHT 



Light is the agent which, by its action on the retina, 

 excites in us the sensation of vision. All bodies, as well 

 as the celestial spaces, are filled by an extremely subtle 

 elastic medium, which is called the luminiferous ether. 

 (Ganot). The luminosity of a body is due to rapid 

 vibrations of its molecules. These vibrations are com- 

 municated to the ether and through it to the terminals 

 of the optic nerve in the retina. 



Sources of Light. The chief source of light is the 

 sun ; but light is obtained by chemical combination, heat, 

 electricity and phosphorescence. Heat produces light 

 only when bodies have their temperature raised to five 



