102 SCIENTIFIC METHOD IN PHILOSOPHY 



for, though the other world is given while the physical 

 world is inferred, to us now the world of physics is the 

 more familiar, the world of pure sense having become 

 strange and difficult to rediscover. Physics started from 

 the common-sense belief in fairly permanent and fairly 

 rigid bodies tables and chairs, stones, mountains, the 

 earth and moon and sun. This common-sense belief, 

 it should be noticed, is a piece of audacious metaphysical 

 theorising ; objects are not continually present to sensa- 

 tion, and it may be doubted whether they are there when 

 they are not seen or felt. This problem, which has been 

 acute since the time of Berkeley, is ignored by common 

 sense, and has therefore hitherto been ignored by 

 physicists. We have thus here a first departure from 

 the immediate data of sensation, though it is a departure 

 merely by way of extension, and was probably made by 

 our savage ancestors in some very remote prehistoric 

 epoch. 



But tables and chairs, stones and mountains, are not 

 quite permanent or quite rigid. Tables and chairs lose 

 their legs, stones are split by frost, and mountains are 

 cleft by earthquakes and eruptions. Then there are 

 other things, which seem material, and yet present almost 

 no permanence or rigidity. Breath, smoke, clouds, are 

 examples of such things so, in a lesser degree, are ice 

 and snow ; and rivers and seas, though fairly permanent, 

 are not in any degree rigid. Breath, smoke, clouds, and 

 generally things that can be seen but not touched, were 

 thought to be hardly real ; to this day the usual mark 

 of a ghost is that it can be seen but not touched. Such 

 objects were peculiar in the fact that they seemed to dis- 

 appear completely, not merely to be transformed into 

 something else. Ice and snow, when they disappear, are 

 replaced by water ; and it required no great theoretical 



