24 



MK. ALFEED NEWTON ON THE POSSIBILITY OF 



even of the most carefully drawn-up lists. And yet, setting aside 

 the immense difference there may exist between personal powers 

 and opportunities of observation, to what two men will these phrases 

 convey exactly the same meaning ? Now I confess I know not in 

 what way such records can be reduced, so to speak, to a common 

 standard, save by expressing them in figures ; nor how they can be- 

 come generally useful unless they are understood in one and the 

 same sense. It is far from my wish to depreciate such observations, 

 and I say this to guard against misapprehension. Nay, I say 

 more, if they are not taken for more than they are worth, they 

 are highly useful ; but only as a basis for future and more complete 

 inquiries. In their present state, as it seems to me, there is no 

 denying that they are imperfect. To take, for instance, an ex- 

 ample from that branch of Zoology of which I am least ignorant. 

 A Devonshire and a Durham ornithologist in a local list of birds 

 would probably each return PJiyllopneuste trochilus and P. rufa 

 as "common." But were they to change places, the previous 

 experience of each would, in a very short time, convince them that 

 whereas, in the southern county, the latter species may double the 

 former in numbers, in the northern the proportion might be ex- 

 actly reversed. Now there are not very many people who have 

 the chance of personally comparing for any sufficient time the pro- 

 portionate numbers of the summer warblers on the banks of the 

 Tamar and of the Tees. Besides, too, there is perhaps the natu- 

 ralist resident perforce in Derbyshire who would fain institute a 

 comparison between his own observations and those taken in 

 Devonshire and Durham. The case becomes still more hopeless 

 when we turn to foreign countries, and, referring to the duchy of 

 Darmstadt or the province of Dauphiny, attempt to ascertain the 

 relative abundance therein of the species I have named. 



Having thus briefly indicated the existing want of any such 

 standard whereby local observations may be compared, I turn to 

 the advantages which seem likely to follow the practical rendering 

 ofthissugge tion. As chief among them (and the only one I w ill 

 here adduce) I would place the Light which might in consequence 

 be thrown upon what we have Lately beard ho much of, the great 

 question of the " struggle for life." It appears to me that 

 before we can assign any cause for the predominance of any ono 

 ipecies over another in any given district, the first thing to bo 



Bftained IS the measure of dial, predominance. This found, if 



the relative abundance of other species which influence its well- 

 being — say, of insects or plants as affording it food and harbour, 



