32 GENERAL VIEW AND BASIS OF SCIENTIFIC RESEARCH. 



. 



latter force is a very feeble one in comparison with the 

 other powers (see page 24) ; it requires the mass of the 

 entire earth in order to attract an ounce with the force of 

 an ounce, whilst a magnet may be made to attract and 

 support many times its own weight. The heat evolved by 

 the sun is calculated to be 2,000 million times as great 

 as that received by the earth from it ; and the light 

 to be 300,000 times greater than that of the moon, or 

 2,200 million times more intense than that of a Cen- 

 tuari. Lalande calculated that it would require more 

 than 17 millions of millions of years to bring about 

 the contemporaneous conjunction of the six great 

 planets. 



'The amplitude of the aerial particles' (of sound- 

 waves) c is less than a 10-millionth of a centimetre.' l A 

 wave of light does not exceed 150,000th of an inch in 

 breadth. In perceiving the sensation of violet colour, 

 707 millions of millions of vibrations are communicated 

 to our eyes in one second of time. 2 The least ray of 

 light also, falling upon a coloured or dark body, is ab- 

 sorbed, and must produce some effect; and the effect is 

 probably more or less different in every different sub- 

 stance, and in the same substance at every different 

 temperature. In a vacuum it repels bodies, in black sub- 

 stances it produces heat, in selenium it alters the electric 

 conductivity, in salts of silver it changes the chemical 

 state, and so on. It has been truly remarked, 4 There is 

 every reason to believe, from the spectra of the elements, 

 and from other reasons, that even chemical atoms are very 

 complicated structures. An atom of pure iron is pro- 

 bably a vastly more complicated system than that of the 



1 Lord Raleigh, Proceedings of the Royal Society, vol. xxvi. p. 248. 



2 Young's Lectures on Natural Philosophy, ii. 267. 



