The Scottish Naturalist. 73 



another remark in caveat of mistaken criticism. Polarity- 

 broaches no physical theory. It is simply an empirical law, 

 or law of observation, declaring that the facts are so-and-so, 

 but saying nothing as to why they are. Therefore, when Mr. 

 Wallace speaks of it as " a hypothesis put forward to account for 

 the abundance of generic forms at an early period and at 

 present," and as " a cause so obscure and hypothetical," and so 

 on, he is in a second point wide of the mark. Polarity is no 

 " occult cause " suggested for any phenomena. It is no cause 

 at all. It only affirms a certain arrangement of the phenomena 

 concerned. It is the mode of the operation of some cause. It is 

 an effect needing itself by some cause to be accounted for. 

 Nay, as we shall bye-and-bye find, we may turn on Mr. 

 Wallace and ask, Is not the vera causa, called Natural Selec- 

 tion, of which part paternity is due to you, the very cause that 

 will account for it? 



But before bringing polarity and natural selection further into 

 line with each other, there is another objection alleged by Mr. 

 Wallace, that would effectually save any trouble about a physical 

 cause of the arrangement which Forbes thought he had observed. 

 " I would, also," says Mr. Wallace, " suggest some reasons 

 against the very nature of the theory of Professor Forbes." 

 These reasons are tantamount to the well-known objection often 

 drawn against other positions, from the incompleteness of the 

 palseontological record. Polarity, he says, assumes the com- 

 pleteness of our knowledge of the life that has existed on the 

 earth, an assumption fatal to it, for that knowledge is infmitesim- 

 ally small. Now, as the theory professes to rest on the facts 

 that are known — to be a reading of the data actually in hand — 

 it would have been relevant and effective criticism to have 

 shown that these known facts do not countenance the theory, 

 or that they are misinterpreted by it. But Mr. Wallace does 

 not proceed in that manner. He appeals against the theory to 

 the vast body of the facts that are unknown — of the data not yet 

 come to hand, but only possible ; which is, in the first place, a 

 very positive way of using negative evidence ; and, in- the 

 second place, would put an arrest on all generalised conclusions 

 from the only geological premises now or ever to be within our 

 reach. 



( To be continued. J 



