The question therefore recurs, What are Dreams? Whence do they arise? We believe that the ideas and emotions which take place in the dreaming state may be ascribed to a twofold origin. They may arise from certain bodily sensations, which may suggest particular trains of thought and feeling; or they may be derived from the operations or activity of the thinking principle itself; in which case they are purely mental. The celebrated Dr. James Gregory--whose premature death was a great loss to science--states, that having gone to bed with a vessel of hot water at his feet, he dreamed of walking up the crater of Mount Etna, and felt the ground warm under him. He likewise, on another occasion, dreamed of spending a winter at Hudson's Bay, and of suffering much distress from intense frost; and found, when he awoke, that he had thrown off the bed-clothes in his sleep, and exposed himself to cold. He had been reading, a few days before, a very particular account of this colony. The eminent metaphysician, Dr. Reid, relates of himself that the dressing of a blister, which he had applied to his head, becoming ruffled, so as to produce pain, he dreamed that he had fallen into the hands of a party of North American Indians, who were scalping him. These were dreams suggested by sensations which, were conveyed from the surface of the body, through the nerves, until corresponding impression was produced on the mind. Upon the same principle, very strong impressions received during the day may modify and very materially influence the character of our dreams at night. Dr. Beattie states that once, after riding thirty miles in a very high wind, he passed a night of dreams which were so terrible, that he found it expedient to keep himself awake, that he might no longer be tormented with them. "Had I been superstitious," he observes, "I should have thought that some disaster was impending; but it occurred to me that the tempestuous weather I had encountered the preceding day might be the cause of all these horrors." Other and less obvious causes are in constant operation. A change in the weather--in the electrical state of the atmosphere--and its barometrical pressure--the temperature of the bedroom--arrangements of the bed-furniture--the adjustment of the bed-clothes--nay, the position of the sleeper, particularly if he cramp a foot or benumb an arm, will at once affect the entire concatenation and issue of his dreams.