848*
THE POPULAR SCIENCE MONTHLY.
In the course of his experiments on the psychic development of a litter of puppies. Prof. Wesley Mills remarked that these animals, as well as those of several other kinds, even on their first day would not creep off from a surface on which they were resting if it was elevated a little distance above the ground. "When they approach the edge, they manifest hesitation, grasp with their claws or otherwise attempt to prevent themselves falling, and it may be cry out, giving evidence of some profound disturbance of their nervous system." But a water tortoise he had had for some years would at any time walk off from a surface on which it was placed. Prof. Mills accounts for the difference by supposing that land animals, depending on a firm substratum beneath them, have inherited "a sense of support"; while the amphibious tortoise is accustomed frequently to drop off from logs into water, and has not, or but little, "sense of support." Then, again, he finds the sense of support "well marked in birds that drop themselves into 'thin air,'" Birds, however, need the "sense of support" when depending on their feet quite as much as land animals.
The instruments used in the observations of the British Association's committee on earth tremors are so delicate that an angle can be detected corresponding with that subtended by a chord an inch long of a circle one thousand miles in radius.