Page:Popular Science Monthly Volume 7.djvu/517

Rh are kept at the Observatory, and two Professors of Mathematics were employed on duties other than those of observing.

volume is an interesting contribution to the literature of an important branch of meteorology. It is a result of many years of observation, and the conclusion of the author is that existing theories of the nature and laws of changes of weather are intrinsically erroneous. Instead of an area of barometric depression being the storm itself, and the cause of the movement of the air-current, the storm is the conflict of air-currents of different temperatures, and the barometric depression the effect of their movement. Hence atmospheric appearances and phenomena more truly indicate and forecast storm-movements than does the barometer.

The air-currents arise primarily from difference of temperature in the equatorial and polar atmospheres, and in the upper and lower regions of air. In the tendency to restore and maintain the equilibrium thus disturbed originate all the movements known as storms.

These movements will be—1. Vertical, that is, between the lower and upper strata of air. 2. Horizontal, or between the poles and equator.

By these movements, in connection with local circumstances, all modifications of storms are produced. In temperate regions the horizontal movement of storms is most frequent—the vertical most frequent and violent in the tropics.

The formation of a cloud tells us not only that vapor is being condensed in the air, but that warm and cool currents have encountered each other.

In the horizontal movement, the cold and warm currents overlap each other, the vapor-laden warm air from the equator rising over the colder current. A consequence is, the warm air ascends until its waves reach an elevation where condensation takes place along their crests, producing flecks and bars of cloud-caps of the aerial waves. These bars of cloud sometimes span the heavens, rising in the southern horizon, heralding the approach of a northeast storm.

Not until these reach the zenith, says the author, does the barometer announce the approaching change. The storm-area is where these opposing currents encounter each other. The rotary theory of storms he considers defective, and says that the wind blows in all parts of a storm-area in direct lines from the circumference to the centre. So we encounter wind from different directions as the storm passes.

According to the author, observation of the clouds, which are an embodiment of the storm, affords earlier and more trusty data of its approach than the barometer, and the rules for navigators based on the cyclone theory are worse than useless. The theory that storms progress by working their own way, that is, by condensation and rainfall in their front, he says is like a wheelbarrow drawing the man after it.

The work is, in many respects, suggestive, and will be read with interest.

thin pamphlet of some 55 pages is really but a fragmentary sample of the long-expected quarto report of the Government surveys of this singularly wild and interesting field. Thus a few specimen full-page plates are given, especially of the weird-like canons; also a map. The plan of composition is commendably judicious, in that it avoids the journal form; for although it is much easier to sustain a certain sort of interest by means of the narrative method, yet in a scientific work such a form is in great danger of unprofitable extension. Still the story is told in a graphic way, with the results classified, thus giving plan and system, which are indispensable to scientific work. As a sample of the best sort of scientific work, for the reason that it is