INTRODUCTION. 



THE SECONDARY MECHANICAL SCIENCES. 



IN the sciences of Mechanics and Physical Astro- 

 nomy, Motion and Force are the direct and 

 primary objects of our attention. But there is 

 another class of sciences in which we endeavour to 

 reduce phenomena, not evidently mechanical, to a 

 known dependence upon mechanical properties and 

 laws. In the cases to which I refer, the facts do 

 not present themselves to the senses as modifi- 

 cations of position and motion, but as secondary 

 qualities, which are found to be in some way 

 derived from those primary attributes. Also, in 

 these cases, the phenomena are reduced to their 

 mechanical laws and causes in a secondary manner; 

 namely, by treating them as the operation of a 

 medium interposed between the object and the 

 organ of sense. These, then, we may call Secondary 

 Mechanical Sciences. The sciences of this kind 

 which require our notice are those which treat of 

 the sensible qualities, Sound, Light, and Heat; that 

 is, Acoustics, Optics, and Thermotics. 



It will be recollected that our object is not by 

 any means to give a full statement of all the addi- 

 tions which have been successively made to our 

 knowledge on the subjects under review, or a com- 



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