ent seasons and in different hours of the day, and is considerably dependent on various meteorological conditions.
It varies with the Locality.—It is more abundant in the country than in the city; by the sea-side than inland; among mountains than in valleys; in well-drained neighborhoods than in those where such sanitary provisions are disregarded. The opposite results of different observations in different localities are accounted for in part by the fact that the amount of ozone is not everywhere constant. Ozone is not often found in closed rooms or chambers. Those who stay in-doors are deprived both of atmospheric electricity and ozone. Like electricity, it increases with the altitude; hence we may in part explain the beneficial effects of mountain-air. The air of the sea is richer in ozone than the air of the land, because evaporation is attended with the simultaneous development of oxygen and ozone. Hence it is that tests applied over the surface of the sea or of lakes, ponds or rivers, show a deeper tint than tests applied over the land. An excess of sea-air will blight vegetation in the vicinity of the ocean; delicate fruits, as the peach and the plum, are cultivated only with difficulty. It has been observed that a prolonged storm coming from the sea will blight vegetation. Possibly the excess of ozone may be a factor in this destruction.
It varies with the Season.—Ozone, like electricity, is more abundant in the winter than in the summer. Atmospheric ozone is not measured with the same accuracy as atmospheric electricity, and therefore the regular gradations during the spring and autumn have not been established as in the case of the latter agent. For the same reason there is much discrepancy among different observers. It is believed that the relatively small amount of ozone in the summer and early fall is due partly to the fact that it is consumed in oxidizing the impurities of the air, and partly to the fact that there is less atmospheric electricity at that time.
It varies with the Hour of the Day.—There is considerable difference in the conclusion of different observations, but the average results seem to show rather more ozone in the atmosphere during the night than during the day. Like atmospheric electricity, ozone rises and falls in pretty regular tides twice during the twenty-four hours. The maximum periods are between 4 and 9 a. m. and 7 to 9 p. m. The minimum periods are between 10 a. m. and 1 p. m. and between 10 p. m. and midnight. It will be seen that ozone is at its minimum when the sun is at the zenith, and its maximum about sunrise and sunset. It varies with atmospheric conditions, as electricity, rain, fog, thunder-storms, snow, wind, clouds, halos, and auroras, eclipses, etc. There is a certain correspondence between the tides of electricity and of ozone; they seem to rise and fall together. This will be apparent on comparing the statements made above. A comparison between atmospheric ozone and electricity has been made by Quetelet, who has given the subject special attention. His obser-
