That this is the source of our fellow-feeling for the misery of others, that it is by changing places in fancy with the sufferer, that we come either to conceive or to be affected by what he feels, may be demonstrated by many obvious observations, if it should not be thought sufficiently evident of itself. When we see a stroke aimed and just ready to fall upon the leg or arm of another person, we naturally shrink and draw back our own leg or our own arm; and when it does fall, we feel it in some measure, and are hurt by it as well as the sufferer. The mob, when they are gazing at a dancer on the slack rope, naturally writhe and twist and balance their own bodies, as they see him do, and as they feel that they themselves must do if in his situation. Persons of delicate fibres and a weak constitution of body complain, that in looking on the sores and ulcers which are exposed by beggars in the streets, they are apt to feel an itching or uneasy sensation in the correspondent part of their own bodies. The horror which they conceive at the misery of those wretches affects that particular part in themselves more than any other; because that horror arises from conceiving what they themselves would suffer, if they really were the wretches whom they are looking upon, and if that particular part in themselves was actually affected in the same miserable manner. The very force of this conception is sufficient, in their feeble frames, to produce that itching or uneasy sensation complained of. Men of the most robust make, observe that in looking upon sore eyes they often feel a very sensible soreness in their own, which proceeds from the same reason; that organ being in the strongest man more delicate, than any other part of the body is in the weakest.