1 86 1 ] Idea of a Bird- Census. 1 5 1 



and collect data ? I hardly think that without such an organization 

 there would be a sufficiency of witnesses. 



Your "diligent" friend thanks you sincerely for the compliment, 

 and for the lift you have given to his scheme. I often think how little 

 would have been accomplished without your constant assistance. 



By-the-by, I ought to tell you that Watson has a chapter on what 

 he calls the "Census of Species," his test of frequency being simply 

 the number of districts inhabited by the several species. Thus he 

 places at the head of the list, as commonest, a plant that occurs in, 

 say, 100 out of 112 districts; next come those species which occur 

 in 99, and so on, down to the plants restricted to one district. I think 

 you should notice this in your paper to Linnaean, because you lay 

 stress on density, he on range. 



Again, April nth. "I cannot get the idea of your 

 proposed Zoological Census out of my head. The plan 

 seems something so vast. I shall look for your paper to 

 Linnaean with the greatest impatience. . . . Do advocate 

 the tracing out of the distribution of our whole Fauna on 

 one uniform system while you are writing on the census 

 (or density of population) question. Would it not be far 

 best to conform to Watson's Provinces, as being judiciously 

 laid down and in use, so as to be able to compare the 

 range of plants and animals ? I have often urged this 

 upon Bell and others, as well as in the review of Cybele 

 Britannica in the ' Annals ' for July, 1860. Do lend me 

 your support, if you are of the same opinion. I fancy Bell 

 and the old hands think no sufficiently general interest is 

 felt in the matter. (You know, I dare say, that I worked 

 out the Butterfly distribution on Watson's plan.) Yet here 

 (with distribution and census) are just the points which 

 admit of novel inquiries into the well-known branches of 

 our Fauna. What a chance of giving a fresh interest and 

 a useful occupation to the many Field Naturalists, who 

 think they have nothing worth recording. 



" I am not sure but what Chaffinches and Yellow Ham- 

 mers are as plentiful here as any bird. I almost think 

 they exceed the Sparrow in numbers." 



His desire for systematic observations on the Migration 

 of Birds, which he lived to take a part in carrying out, 

 appears in a letter dated December 6th, 1861. He was on 

 the point of going up to London to meet the members of 

 the B. O: U. 



