or the wettings due to driving snow or rain. Whenever the barometer sinks very low, heads begin to ache, and sleep to forsake all the considerable class of people whose nerves require the stimulus of a high pressure to discharge their functions with their usual rapidity and punctuality. There are people who can hardly sleep at all at a height of five or six thousand feet, and though, of course, no fall of the barometer, even in a hurricane, approaches in any degree to the fall which is due to this elevation, there appears to be something in the irregularity of the pressure, when a gale sweeps at the rate of sixty miles an hour over the earth, and the mercury stands one day at only 28 or 27 1-2 inches in the tube of the weather-glass and at 30° the next, that more than compensates for the mere diminution of the weight of air which you get in high Alpine situations. Now that we know that the mere presence, possibly the mere pressure, of light will so far alter the constitution of a substance like selenium as to turn it from a very poor conductor of electricity into a very decent one, we need not be surprised to find that sudden changes in the conditions of atmospheric pressure often lead to changes in the physical constitution of the nerves that are accompanied by both great distress and great loss of power. But so much the more we have reason to be very thankful that these great disturbances in all the conditions of life do not effect the physique of the brain even more than they actually do. Very slight forces seem to have so great an influence on the molecular structure of certain substances, that it is wonderful our nerves should not be more liable than they are to cerebral storms and hurricanes,—to disturbances, for instance, which might make whole populations temporarily delirous, and turn a city into a big lunatic asylum, instead of a merely harried, and worried, and wetted population. Indeed, when we think of the wonderful volatility of the atmospheric shell in which we live, it is certainly much more surprising that we do not suffer oftener and worse from its high and low tides, its tempests and its stagnations, than that we are now and then forced into grumbling at the excesses from which we are generally so free.
"MYSTERIOUS SOUNDS."
The effect of certain sounds upon the mind is often very curious. We do not allude to the ordinary phenomena of speech, singing, and music, where the sound-producing apparatus is tolerably familiar, and its distance from the hearer estimated with a near approach to accuracy. The effect is only "mysterious" when there is any doubt as to where the sound comes from, and how it has originated; the imagination then begins, and sometimes works itself up to very singular hallucinations. Night, or darkness without night, has much to do with this matter. When we cannot see the sound-producing agent, conjecture is apt to run wild; and ghost-stories often depend on no better foundation than this. For instance, certain sounds may frequently be heard at night, coming from the air above, but from an invisible source—a kind of whistling or prolonged cry, the producers of which are known in certain parts of England as "whistlers." Some legends make it out that these whistlers are ghosts, some evil spirits, some Wandering Jews. But the truth is that the sounds proceed from birds, such as wild geese or plovers, which are in the habit of flying in flocks by night, either for the purpose of reaching distant feeding-grounds, or during their annual migrations. The cry which is usually uttered by the "leader" during these nocturnal bird-flights has, from ignorance of its cause, been regarded as weird and mysterious by superstitious folks, who associate it with impending evil.
Sir David Brewster gives an excellent account of a mysterious night-sound which would have frightened many persons, but which proved innocently harmless when tested by a steady observer. A gentleman heard a strange sound every night, soon after getting into bed; his wife heard it also, but not at the time when she retired, a little earlier than he. No probable cause could be assigned; and the effect upon the imagination became rather unpleasant. He found, some time afterwards, that the sound came from a wardrobe which stood near the head of his bed. He almost always opened and closed this wardrobe when undressing; but as the door was a little tight, he could not quite close it. The door, possibly affected by gradual changes of temperature, forced itself open with a sort of dull sound which was over in an instant. From the lady not being in the habit of using that wardrobe, the mys-
