who will measure the height above the ground and report it to the Signal Office. The measuring rod is graduated in inches and tenths of inches, and the proportion between the cylinder and funnel is as one to ten, so that ten inches upon the rod correspond with one inch of actual rainfall, one inch to one-tenth of rain, etc." Snow is directed to be melted and reported as rain, the fact of its being melted snow being carefully noted. When from any cause the snow cannot be melted its depth will be measured, and ten inches of snow reported as one inch of rainfall, the fact of its being so approximated being also noted.

In regard to the appearance of the sky, observers are instructed to report the weather as clear when the sky is three-tenths, or less than threetenths, covered with clouds; fair when the sky is from four-tenths to seven-tenths (inclusive) covered; and cloudy when the sky is more than seven-tenths covered.

The ingenious system of forwarding detailed reports at a minimum expense to the Government by using cipher words (such as "hub," which means a thunder-storm with light rain, wind blowing from the north," or "rage," which indicates "rainfall since last report has been nineteen one-hundredths of an inch") is no doubt more or less familiar to our readers.

Besides the causes ordinarily enumerated as producing the atmospheric vicissitudes upon our globe and referred to in the body of this work, such as the motion of the earth upon its axis and the obliquity of that axis to the plane of the ecliptic, we have another fact, the importance of which has only been recognized within the last few years, and that is the movement of areas of low barometer across the surface of the earth, the consequences of depressions or furrows in the surface of our atmosphere. These areas of low barometer have a general tendency to move over us from west to east. As a rule, therefore, when the area of low barometer is west of us we may expect a storm, and although this storm may pass by us, either nearer to or further from the North Pole than the spot we occupy, without causing our neighborhood any great disturbance, it is almost certain to cross our meridian at some point. After that transition has been effected the winds, following as they do the course of such a depression in our atmosphere, will blow over us in an easterly direction, varying to the northeast or to the southeast, perhaps, according as the storm-centre happens to be travelling above or below our parallel of latitude. The clouds will of course be blown along from the west by the winds which are hurrying across toward the area of low barometer, which has now progressed to the eastward of our station, and after a few hours or a day, depending upon the magnitude of the cloud accumulation, we will see the blue sky again, and know that this particular storm is over.

Although we usually find that it takes three or four days for another area of low barometer to reach our individual locality, we must remember that there is no absolute certainty about the distance between these centres of storms. Another low-barometer area may advance upon us in one or two days, or, on the other hand, the one next following may progress so slowly, or may be diverted from its track in such a way that it may not come to us for five or six days, and when it does arrive, attack us from another and totally different direction.

The path of an area of low barometer across the country has been rather fancifully yet aptly compared to the track of an immense watercart, the centre of which is of course the line of most violent storm. The average rate of such a storm-centre is, according to Prof. Loomis, 26 miles

per hour, the mean velocity in summer being 21 miles and in winter 30 iniles, but the rapidity with which it moves is very variable, and may attain to 50 miles an hour or 1,200 miles in the twenty-four.

Winds, as a general rule, tend toward the area of low barometer as a centre, but ranges of mountains, valleys, extensive forests, and so forth, often produce local variations in the direction of these converging currents of air. In violent storms the winds tend to circulate about the stormcentre also in a direction contrary to the motion of the hands of a watch. From this it will be at once perceived that when an area of low barometer happens to be crossing our continent at its upper part, the winds felt in places along its centre will be in a general way from the south, and vice versa. That is to say, if at any time an area of low barometer is passing through New York and New England, the winds in Philadelphia will be toward it, and for twelve hours, perhaps, from the southeast, then for another twelve hours nearly south, afterward veering round still further until a southwest or finally a westerly wind brings us clear weather. On the other hand, if a similar storm-centre is travelling through Virginia and Maryland, the winds in Philadelphia will be northerly, and generally cooler.

The apparent exceptions to the rule of north winds being cooler and south winds warmer are obviously due to large volumes of warm air or of cold air, respectively, having previously been blown to the north or south of a particular position.

Although the general direction of movement of the areas of low barometer seems to be around the earth, in the direction of our planet's motionthat is, toward the apparently rising sun-their course may sometimes vary very widely from this, and, as shown by the maps, they may occasionally travel almost due north for three or four days, during which time they traverse a distance perhaps of 1,000 or 1,500 miles before they resume their normal easterly tendency.

Since, therefore, the storm-centre is in the neighborhood of the area of low barometer, there is seldom or never a true northeast storm, much as we hear people talk about "northeasters." A northeast wind with rain in any particular locality results usually from an area of low barometer travelling eastwardly a few hundred miles south of that position.

By making use of the daily predictions, or still better of the daily weather maps where they are accessible, as general guides, and correcting these for individual localities by a study of the local winds, clouds, and sunsets, and especially by observing a mercurial or aneroid barometer, noting its fall as an indication of the approach of an oncoming area of low barometer toward the exact spot on which we live, and also especially observing when and how rapidly it rises as a token that the low area (which is the storm-centre) has passed by us, it is, I believe, possible to attain an accuracy in predicting the weather which appears to unscientific persons almost miraculous, and secures for us as practical Hygienists immense advantages, both to our own health and to that of our patients.

VENTILATION AND WARMING.

BY D. F. LINCOLN, M.D.

THE subjects of ventilation and heating have to be studied, in America, from a point of view somewhat differing from that taken in England. As regards the requirements of cubic space and supply of fresh air, there is and can be no difference. But in certain respects, for example as regards the standard of temperature to be maintained, we find ourselves unable to adopt English rules, and the English would be equally unwilling to accept ours. The severity of our seasons, too, has forced us to make use of steam and stoves to a much greater extent than is usual in England, while the old-fashioned method of warming by the fireplace has fallen too much into disuse among us.

HOT-AIR FURNACES.

When the inmates of a private house seek comfort, their first thought of improvement is in the direction of increased warmth. The halls are to be made as warm as the rooms; the sleeping-rooms are to made comfortable for occupancy by day; and to effect this purpose, a furnace in the cellar is the most feasible means, if the house be of moderate size. A house of more than three large rooms on the ground floor, however, with one or two stories of rooms above, cannot be properly heated by one furnace (Philbrick). However powerful the apparatus, it is unsafe to try to conduct heated air more than six feet in a horizontal direction from the furnace. Neither should we attempt to conduct a hot-air flue against the direction of the prevailing wind, in exposed situations. If a windward room cannot be warmed, because the furnace air refuses to enter it, the remedy is to open a chimney flue in the room; it may be necessary to light a fire to increase the draught of the chimney. Air cannot be forced into a tightly closed room: a failure to warm such a room is remedied by opening a discharge for the air from it. Flues supplying different rooms. sometimes "draw against each other," as chimneys will; this is likely to occur when the supply from below is not sufficient for all, either because the air-box, or inlet of fresh air to the furnace, is too small, or because after it has been closed in a high wind some one has neglected to open it. A most eccentric effect is sometimes produced when a current of hot air passes out of the orifice for supplying fresh air to the furnace, while the air is sucked downward from the rooms.

The best way to heat a house at moderate expense seems to be by a combination of hot-air furnace in the cellar, and open fireplaces in the rooms. The false fireplaces, with dummy mantels, which take the place of the true in cheap houses, violate not only the principles of taste, but the laws of ventilation. An open fireplace in a closed room is very useful, not VOL. II.-30