CHAPTER Xltl, 



COLOUR. 



Undulation theory of colour What is the force which governs colour 

 Primary causes overlooked as usual Great display of Arithmetic- 

 Looseness in Science When we will freeze to death Portland 

 Scientific Convention Tyndall on the vibratory theory 474,439,- 

 680,000,000 red waves a second This theory questioned No colour 

 on the Earth Herschell Hclmholtz Science like a voyage of dis- 

 covery We introduce the atomagnetic theory of colour Colour * 

 pfoperty of matterColours of mineral flames Why is the sky 

 blue ? Tyndall's " Scientific use of the Imagination "The setting 

 sun red The hills purple. 



HAVING given the cause of light, and its modes of action in 

 different forms, we now give an explanation of that element of 

 it which we reserved for a chapter to itself, 



As light has been explained by the theory of undulation, so 

 also has colour, which in ono way is inseparable from it. 



The theory is said to have been siiggested by the vibration of 

 a harp string. The shorter the string is made, the greater are 

 the number of vibrations produced by the same force ; and the 

 shriller the note becomes. 



Thus it is said to be with colour. Light vibrates, but 

 coloured lights vibrate more. 



From experiments made, it has been shown that red rays are- 

 propagated the shortest distance, and violet rays the longest 



