ANALOGY WITH FICTION AND BIOGRAPHY. 101 



of a real man reduce him any nearer to the imaginary being 

 of a novel. To the last, the division between fiction and 

 biography remains an impassable gulf. So, too, remains the 

 division between the Science dealing with the inter-actions 

 of hypothetical bodies in space, and the Science dealing 

 with the inter-actions of existing bodies in space. &quot;We may 

 elaborate the first to any degree whatever by the intro 

 duction of three, four, or any greater number of factors under 

 any number of assumed conditions, until we symbolize a 

 solar system ; but to the last an account of our symbolic 

 solar system is as far from an account of the actual solar 

 system as fiction is from biography. 



Even more obvious, if it be possible, does the radical cha 

 racter of this distinction become, on observing that from the 

 simplest proposition of General Mechanics we may pass to 

 the most complex proposition of Celestial Mechanics, with 

 out a break. A\ r e take a body moving at a uniform velocity, 

 and commence with the proposition that it will continue so 

 to move for ever. Next, we state the law of its accelerated 

 motion in the same line, when subject to a uniform force. 

 We further complicate the proposition- by supposing the 

 force to increase in consequence of approach towards an 

 attracting body ; and we may formulate a series of laws of 

 acceleration, resulting from so many assumed laws of in 

 creasing attraction (of which the law of gravitation is one). 

 Another factor may now be added by supposing the body to 

 have motion in a direction other than that of the attracting 

 body ; and we may determine, according to the ratios of the 

 supposed forces, whether its course will be hyperbolic, para 

 bolic, elliptical, or circular we may begin with this hypo 

 thetical additional force, as infinitesimal, and formulate the 

 varying results as it is little by little increased. The problem 

 is complicated a degree more by taking into account the 

 effects of a third force, acting in some other direction ; and 

 beginning with an infinitesimal amount of this force we may 



