Similar variations also take place in the horizontal force, as evinced by the action of the magnetometer needle, and in the vertical force, as shown by the oscillations. So that it is evident that there are two maxima, and two minima of magnetic activity every day, shown by all the methods by which we measure magnetic action and force--more than double at the acme of northern summer transit over that of winter, and proceeding _pari passu_, with the other daily phenomena--evincing the same irregular action which the other phenomena evince. Still another phenomenon, which has a daily change, is electric tension, or the increase or decrease in the tension of the positive or true atmospheric electricity. [Illustration: Fig. 19.] The following table shows the mean two hourly tensions for three years, at Kew, viz.: Hours 12 P.M. 2 A.M. 4 A.M. 6 A.M. 8 A.M. 10 A.M. Number of observations 655 784 804 566 1,047 1,013 Tension 22.6 20.1 20.5 34.2 68.2 88.1 Hours 12 A.M. 2 P.M. 4 P.M. 6 P.M. 8 P.M. 10 P.M. Number of observations 848 858 878 874 878 1,007 Tension 75.4 71.5 69.1 84.8 102.4 104 From this it will be seen that the tension of electricity is at a minimum at 4 A.M., also, that it rises till 10, falls till 4 P.M., but not as rapidly, rises till 10, falls again till 4 A.M., or the close of the meteorological day--having two maxima and minima, as have most of the phenomena thus far considered. In order to see what the connections between these ever-present, daily phenomena are, and their connection with other phenomena, and that we may understand their normal conditions, I will trace them approximately in a diagram (figure 17.) The foregoing diagram of the daily phenomena of a summer's day, when no disturbing causes are in operation, no storm existing within influential distance, and no unusual intensity or irregular action of any of the forces present, affords a basis for considering the various phenomena of the weather in all its changes and conditions. It is obvious that the other phenomena do not all depend upon temperature merely, if indeed any of them do. Temperature has but one maximum and minimum, and that is exceedingly regular, and does not correspond with any other. The barometer has two; electric tension, two; magnetic activity, two; condensation, two--one the formation of cloud, and the other the formation of fog and dew; wind, one--resembling temperature in that respect, but embracing a much less period. Fog forms at one barometric minimum, and cloud at another. Fog forms at one period of the magnetic variation, cloud at another. The formation of cloud corresponds with the greatest intensity of magnetic action, and its associate electricities. But the oscillations of the barometer do not correspond with either. And thus, then, we connect them: