26 THE POPULAR SCIENCE MONTHLY, 



uniform. 2. One of the watches might be constantly regulated, so as to 

 keep it uniform with the other. 3. The watchmaker might be so skill- 

 ful as to be able to make both go together, though independent of one 

 another. As between body and soul, the first contrivance is clearly 

 impossible. The second, which agrees with the occasionalist doctrine, 

 is unworthy of God, whom it employs as a Deus ex machina. The 

 third then remains, and here we find again Leibnitz's peculiar doctrine 

 of Preestablished Harmony. 



But these and all similar views are discredited by the more recent 

 investigations of natural science, and are void of all influence in mod- 

 ern thought, by reason of the dualistic principle on which they rest, 

 in conformity to their semi-theological oj-igin. The propounders of 

 these theories start out from the hypothesis of a spiritual substance 

 absolutely diverse from the body, viz., the soul, and their study is to 

 investigate its association with the body. They find that the coupling 

 of these two substances is possible only by a miracle, and that even 

 after this first miracle another association of the two cannot take place 

 except by means of a fresh miracle, or of a continuous miracle, dating 

 from creation. This consequence they give out as a new solution of 

 the problem, though they never took sufficient pains to inquire whether 

 they themselves have not attributed to the soul such a nature that 

 mutual interaction between it and the body is unthinkable. In short, 

 the most satisfactory demonstration of the impossibility of the inter- 

 action of soul and body leaves room to question w^hether the premises 

 were not arbitrary, and whether consciousness may not be regarded 

 as simply the effect of matter, and so perhaps understood. Hence, the 

 student of natural science demands that the argument to show that 

 mental phenomena are unintelligible from their material conditions 

 shall have nothing to do with any hypothesis as to the origin of such 

 phenomena. 



Astronomical knowledge of a material system I call such a knowl- 

 edge of all its parts, their respective positions and their motions, that 

 their position and motion, at any given time, past or future, may be 

 calculated with the same certainty as we calculate the position and 

 motion of the heavenly bodies, by means of previous absolute accuracy 

 of observation and perfection of theory. To get the differential equa- 

 tion whose integration will give the desired results, we need only have, 

 as it were, three positions of the parts of the system ; i. e., we must 

 know the position of the parts of the system at three successive in- 

 stants, separated by two differentials of time. From the difference of 

 the courses run in the equal and infinitesimal periods of time between 

 the three we deduce the forces acting upon the system and within it. 



In our incapacity to comprehend matter and force, astronomical 

 knowledge of a material system is the completest knowledge we can 

 expect to acquire of it. With this our instinct of causality is wont to 

 be satisfied, and this is the kind of knowledge that would be possessed 



