1 86 Life and Matter [chap. x. 



lycopodium-dust, must be a million times 

 bigger still.) Such a grouping is likely to 

 have properties differing not only in degree 

 but in kind from the properties of simple 

 substances. 



For it must not be thought that aggrega- 

 tion only produces quantitative change and 

 leaves quality unaltered. Fresh qualities 

 altogether are liable to be introduced or to 

 make their appearance at certain stages 

 certain critical stages in the building up of 

 a complex mass (cf. p. 71). 



The habitability of a house, for instance, 

 depends on its possessing a cavity of a 

 certain size , there is a critical size of brick- 

 aggregate which enables it to serve as a 

 dwelling. Nothing much smaller than this 

 would do at all. The aggregate retains this 

 property, thus conferred upon it by size, 

 however big it may be made after that ; 

 until it becomes a palace or a cathedral, 

 when it may perhaps reach an upper limit 

 of size at which it would be crushed by its 

 own weight, or at which the span of roof is 



