The thunder storm turns about a horizontal axis instead of a vertical one, as in the case of the tornado. On land thunderstorms occur most frequently at speci fied hours of the day or night, such as 3 to 5 in the afternoon or 9 to 10 in the evening, and sometimes even at 2 or 3 in the morning, but no such periods are observed over the ocean. They occur at any hour of the day or night with equal frequency. In regard to the electrical phenomena of the atmosphere it is not safe to hazard definite statements, but pos sibly auroras are due to earth-captured solar electrons, while the lightning of a thunder storm owes its origin, chiefly at least, to the electrical separation produced by the action of wind on raindrops.
Cold The area and intensity of cold waves depends upon the size of the con tinents and their distance from the equator, The interiors of North America and of Siberia experience more severe cold than occurs at either pole. Departures from the normal tem perature of a time and place are due to the dynamic heating and cooling of the air through its upward and downward motions below the six or seven-mile level. Air heats by COM pression at the rate of about 1° for each Ti feet of descent in the anti-cyclone, but tin heating induces clearness through the evapora tion of clouds and allows a rapid loss of hes by radiation. And then the temperature of the air before it starts on its downward joarcei is so low that notwithstanding the heat of tm pression, it may be extremely cold who e reaches the earth. However, it is difficult .4:
formulate any hypothesis that will fully a: count for the cold of the east side of the sc_i cyclone being so much greater than that of tic west side, or for the heat of the cast side the cyclone being so in excess of that of west side.
Warm In summer there cc= periods of stagnation in the drift of the hid and the lows. At such times if a high iai gishly rests over the south Atlantic Ocean 14 tween Bermuda and the coast of the Uth-e: States and a low over the northern 14-; Mountain region, there will result what popularly known as a warm wave, for the a. will slowly and steadily flow from the sari- east, where the pressure is greater, toward •!.! northwest, where the pressure is less, and, 7 ceiving constant accretions of heat from .1: hot, radiating surface of the earth, finally come abnormally heated. This superheraC condition continues until the high over 1! ocean dies out or drifts away. Consult N. 'Elementary Meteorology' (Boston 1894); Fe re], William, 'Treatise on the Winds' (Neg York 1893) ; Flammarion, 'Thunder and Lie: ning' (Boston 1906); Hann, 'Lehrbuch de: Meteorologic' (3d ed., Leipzig 1914) ; MMar 'Meteorology' (New York 1912) -, M&-r 'Descriptive Meteorology' (ib., 1910); N'ta-, 'Practical Exercises in Elementary Mem ology' (Boston 1899).
Witus LIJTHER Moon. Professor of Meteorology, George Waskitrit:J University.