The above is extracted from the diary kept by my sister. I did not myself witness the progress of this research with the hearth-brush, as I did so many of the other investigations successfully pursued by that wonderful animal. But I have a perfect confidence in the accuracy of my sister’s observation, as well as in the fidelity of her account; and, moreover, the point with which I am about to be concerned has reference to what followed subsequently, as to which I had abundant opportunities for close and repeated observations. For the point is that, after having thus discovered the mechanical _principle_ of the screw in that one particular case, the monkey forthwith proceeded to _generalize_, or to apply his newly gained knowledge to every other case where it was at all probable that the mechanical principle in question was to be met with. The consequence was that the animal became a nuisance in the house by incessantly unscrewing the tops of fire-irons, bell-handles, &c., &c., which he was by no means careful always to replace. Here, therefore, I think we have unquestionable evidence of intelligent recognition of a principle, which in the first instance was discovered by “the most unwearying perseverance” in the way of experiment, and afterwards sought for in multitudes of wholly dissimilar objects.[52] To these numerous facts I will now add one other, which is sufficiently remarkable to deserve republication for its own sake. I quote the account from the journal _Science_, in which it appeared anonymously. But finding on inquiry that the observer was Mr. S. P. Langley, the well-known astronomer, and being personally assured by him that he is certain there is no mistake about the observation, I will now give the latter in his own words. “The interesting description by Mr. Larkin (_Science_, No. 58) of the lifting by a spider of a large beetle to its nest, reminds me of quite another device by which I once saw a minute spider (hardly larger than the head of a pin) lift a house-fly, which must have been more than twenty times its weight, through a distance of over a foot. The fly dangled by a single strand from the cross-bar of a window-sash, and, when it first caught my attention, was being raised through successive small distances of something like a tenth of an inch each; the lifts following each other so fast, that the ascent seemed almost continuous. It was evident that the weight must have been quite beyond the spider’s power to stir by a ‘dead lift;’ but his motions were so quick, that at first it was difficult to see how this apparently impossible task was being accomplished. I shall have to resort to an illustration to explain it; for the complexity of the scheme seems to belong less to what we ordinarily call instinct than to intelligence, and that in a degree we cannot all boast ourselves. [Illustration] “The little spider proceeded as follows:—