I50 Notes, ii. i. 



BOOK IL 



(Ch. 1.) 1. That is, the treatise which by a mistranslation of its title is usually known 

 as the Natural History of Animals ; a mistranslation to which our popular term ' ' natural 

 history " is due. The ordinary title is so sanctioned by use, that I have elsewhere occa- 

 sionally retained it. 



2.. It will be noticed that A. says "such as air earth fire and water," implying 

 apparently that there are more elements than these. In fact he held that there was aT 

 fifth, the quintessence of later writers ; this fifth however, the aether, not entering into the 

 composition of strictly terrestrial objects, but forming the sole substance of the heavenly 

 bodies. To this belief he was led by his views as to motion. He held that all visible motion 

 could be reduced on analysis to three elements, (i) motion round the centre, or circular 

 motion; (2) rectilinear motion from the centre towards the periphery, or upwards; (3) 

 rectilinear motion from the periphery towards the centre, or downwards. Now there is no 

 such thing as motion without a moving body. There must therefore be elementary bodies 

 corresponding to these elementary motions. To the motion upwards fire and, in a lesser 

 degree, air correspond; to the motion downwards earth and, in a lesser degree, water. 

 There is apparently nothing left to correspond to circular motion, which is yet the most 

 perfect motion of all, seeing that a circle is a perfect line, which a straight, line is not. 

 •' From this it is evident that there is in nature some essence of body besides the elements 

 which we have, here, more divine than these and superior to them. For "it is absurd to 

 suppose that motion in a circle can possibly be an unnatural motion, seeing that every- 

 thing which is unnatural quickly perishes, whereas this motion, alone of all, is continuous 

 and eternal. So that from all this we infer with perfect confidence, that besides the 

 elements which we have here and about us there is another removed far off, and the 

 more excellent in proportion to its distance from the things of earth " [^De Ccelo, i. 2 ; 



iii. 3. 5)- 



3. The so-called elements, says A, elsewhere {D. G. el C. ii. 2-3-5), are not simple 

 bodies but compounds, being produced by combinations of the primary forces or active 

 properties of matter. Tangible objects differ from each other in endle'ss ways, as 

 regards colour, taste, smell, etc. {Meteor, 'w'. 10) ; but they are all either fluid or solid, and 

 all either hot or cold. Everything tangible presents two of these properties ; it is either 

 solid or fluid, and either hot or cold. There are then four main elementary properties, 

 and each object possesses two of them. Now among four- things there may be six com- 

 binations of two and two (eruC**^!*") '> but the pairing of two directly opposite properties, 

 as of cold and hot, causes them both to disappear ; for they neutralise each other. Thus 

 only four combinations remain, and these correspond to the four apparently simple bodies, 

 fire, air, water, earth ; solid and hot forming fire ; hot and fluid forming air, for air cor- 

 responds to vapour ; fluid and cold forming water ; cold and solid forming earth. 



EARTH 



Solid 



WATER - - - - { ""rr"' \ FIRE 



Hot 

 AIR 



