270 VARIABLE EFFECTS FROM INVARIABLE CAUSES. 



enon to "be passed lightly by, more especially when we consider the sur- 

 prising results to which it eventually leads in the higher forms of life. I 

 Illustration of sna ^ therefore, without any apology, digress briefly for the 

 the production sa k e o f illustrating my meaning, by showing how, even in 

 suits^yinvari- the material world, from conditions which are as fixed as fate, 

 able causes. through interaction of consequences variable results arise. 



The laws of nature, being founded on pure reason, are absolutely un- 

 changeable. Of the things which are presented to our contemplation, 

 they alone are invariable. Material substances of every kind wear by 

 time, and exhibit incessant alterations, and this the same whether they 

 are of a terrestrial or a celestial kind. There are tides, eclipses, seasons, 

 births, deaths. Throughout the universe there is no monument that re- 

 tains its primordial condition; for all material aggregations are only 

 forms, and every form, in the process of time, must perish. There are 

 changes of the surface of the earth, changes in its position as to the sun, 

 changes in the places of systems of worlds as to one another. Every 

 thing is at every moment in motion ; but in the midst of all, every law 

 of nature, as, for example, the law of gravitation, endures without varia- 

 tion for an instant, and is never for an instant suspended. 



This invariability of natural laws from age to age, even under circum- 

 stances in which we might suspect a change, is illustrated by the parallel 

 which may be traced between the development of the most recent em- 

 bryos, as of man, and those of the ancient geological times, or between 

 human development and that of the whole animal series. In all these 

 cases such a phenomenon is never witnessed as that of a part springing 

 from nothing : it conies out of something existing before, and exists as a 

 consequence of some preceding act. The order in which part arises from 

 part is the same now as it has been in all times the same in organ- 

 isms which are most distinct from each other in structure or position in 

 the natural scale ; and thus we see that development is not only the con- 

 sequence of law, but of law which is unchangeable and universal in its 

 application. 



As with these phenomena of development and all natural facts, so with 

 the operations of the mind. There is no such thing as a spontaneous or 

 self-originating thought. Every intellectual act is the consequence of 

 some preceding act. It conies into existence in virtue of something that 

 has gone before. Two minds constituted precisely alike, and placed 

 under the influence of precisely the same external physical circumstances, 

 must give birth to precisely the same thought. Such is plainly the 

 consequence of that invariability and universality of the laws of nature 

 on which I have been insisting, which is illustrated by the fact we so often 

 witness in our daily affairs, and strikingly in the case of philosophical 

 discoveries, the same idea occurring to many persons at the same time. 



