162 GENERAL VIEW AND BASIS OF SCIENTIFIC RESEARCH. 



in vital science, as physical and mental heredity ; and in 

 psychology, in what has been termed the ' indestructibility 

 of ideas.' l A body, also, passing through a cycle of changes 

 during a given period of time, tends to repeat that cycle 

 of changes ; this is manifest in the motions of all the 

 heavenly bodies, in the recurrence of the sleeping and 

 waking states of plants and animals, of labour and rest, 

 &c. Man's restless spirit, and all the actions of men 

 and animals, may thus be interpreted by the great prin- 

 ciple of persistency of motion. 



V. The universal existence of matter and energy (i.e. 

 matter and energy pervade all space) is another wide 

 principle, and is inferred from the general truth, that all 

 known space appears, from observation and inference, to 

 be occupied by matter of greater or lesser degrees of 

 density ; and from the more special truth, that no man 

 has yet been able to produce a perfect vacuum ; also from 

 these truths, combined with the fact that wherever matter 

 exists, energy has been observed with it. 



VI. Another very general truth may be conveniently 

 termed the universality of motion. Motion is relative ; 

 all the globes of the visible part of the universe (and the 

 bodies upon and within them) appear to be in motion ; and 

 the smaller bodies and particles which occupy the inter- 

 vening space are probably in the same condition. All the 

 molecules of each individual substance, being continually 

 changing in temperature, are never absolutely at rest. As 

 also all the various active forms of energy or forces of 

 nature are considered to be indissolubly connected with 

 different modes of motion of the molecules of matter, there 

 is associated with this great truth that of the universality 

 of active energy. 



VII. Another general principle, termed the dissipa- 



1 See page 65. 



