[Letters to Editor]

Abstract

I BEG to thank Mr. Nicols for his courtesy in supplying the missing links of evidence in the rat cases (NATURE, vol. xix. p. 433), cases which may, I think, be applied with reference to Mr. Henslow's difficulty concerning “abstract mental reflection;” for it seems to me now that the most probable supposition is that the rat-community had learned through experience (likely got accidentally in cutting pipes which obstructed their operations) that such-like pipes at times contain water, and by exercise of reason came to the conclusion that it was worth while to make the exploration in the instances given.