9. "Highs" and "lows" are a consequence of the temperatures and velocities of the upper currents.
Whence it follows that the most important problem of meteorology is the investigation of the causes and consequences of the disturbance of indifferent equilibrium of the atmosphere, and the weightiest problem in weather prediction is the investigation of the geographical origin or extraction of air currents pursuing their course above us toward the pole.
In Pomortsew's treatise on synoptic meteorology, published in Russia, there are full chapters on prediction of weather, whether from synoptic charts, from observations at a single place, or from prognostics of great length based on researches on the succession of warm and cold months. It also contains Pomortsew's investigations on the types of pressure distribution in eastern Europe, as well as the average path of cyclones.
The favorable opportunities afforded by the Eiffel tower have been utilized by French meteorologists. M. Angot states that during the anti-cyclone of November, 1889, the temperature on the tower was several degrees higher than below. The change of weather set in earlier, with a strong and warm wind, on the tower, while the air at the ground was cold and calm. Wind observations on the tower show a ratio of 3.1 at that height (303 meters) to the velocity at a height of 21 meters, as determined from 101 days' observations, which, remarkable at such a small height, discloses the peculiarity of high mountain stations.
Partsch, writing on evidence of climatic changes within historical times in the Mediterranean region, remarks that too much attention has been given to changes in crops, the introduction of plants, and the limits of domestic animals. He states that existing information as to the harvest time of ancient days indicates an unchanged climate, while the land-locked lakes in Tunis, which afford the best evidence on rainfall variation, show absolutely no climatic change.
Van Bebber, in writing on weather types, claims that a line drawn from the center of a cyclone perpendicularly in the direction of the heaviest gradients will in general be perpendicular to the subsequent path of the "low," and that these lows leave high temperature on the right hand.
Hill, in describing hail-stones and tornadoes in India, explains them on the principle of the great diminution of temperature upwards in the air, but a critic, in combating this theory, objects to the high and low stations selected to show temperatures.
The so-called "weather plant" of the tropics has passed through the process of investigation with the usual result. It appears surprising that in these days it should be believed that any plant or animal can foretell weather 48 hours in advance, particularly after considering the vast amount of proof as to the enormous rapidity with which weather-changes progress from day to day.
Hugo Meyer, in treating the precipitation of central Germany for the ten years ending in 1885, pertinently remarks that the same significance does not attach to the same rainfall for all places and different times of the year, for this average value is not the amount most likely to fall in any particular interval of time, since there is a limit to the extent of the negative deviations on one side—that is, 0 or no rainfall, while on the positive side there is no limit. The most probable depth of rainfall, therefore, is less than the mean value, the preponderance of negative over positive deviations being about 10 per cent. and sometimes as great as 20 per cent.