According to observations made by Mr. Crosse, the following statement shows the tendency of the atmosphere, in certain conditions, to thunderstorms. We may accept the deduction of M. Peltier that grey and slate-colour clouds are charged with negative, and white, rose-colour, and orange clouds with positive electricity. The order of arrangement in the following table places the most likely source of thunderstorms first, and the least likely source at the end, with regular rotation of intermediate probabilities intervening:— 1. Regular thunder clouds. 2. Driving fog with small rain. 3. Fall of snow, or hailstorm. 4. Smart shower on a hot day. 5. Smart shower on a cold day. 6. Hot weather after wet days. 7. Wet weather after dry days. 8. Clear frosty weather. 9. Clear warm weather. 10. Cloudy days. 11. “Mackerel” sky. 12. Sultry weather and hazy clouds. 13. Cold damp night. 14. Cold, dry north-east winds. We have thus briefly touched upon some of the atmospherical phenomena directly attributable to electricity. In our articles upon Meteorology we will consider the aurora and many other interesting facts concerning the atmosphere, and the effects of sound, heat, and light upon the air. [Illustration: Fig. 292.—Lightning conductor.] FOOTNOTES: [18] We are indebted for many facts respecting Mr. Edison’s light in this chapter to a paper by Mr. Upton. CHAPTER XXIII. AERONAUTICS. PRESSURE OF AIR IN BODIES—EARLY ATTEMPTS TO FLY IN THE AIR—DISCOVERY OF HYDROGEN—THE MONTGOLFIER BALLOONS—FIRST EXPERIMENTS IN PARIS—NOTED ASCENTS. In the first part of this volume we entered into the circumstances of air pressure, and in the Chemistry section we shall be told about the atmosphere and its constituents. We know that the air around us is composed principally of two gases, oxygen and nitrogen, with aqueous vapour and some carbonic acid. An enormous quantity of carbonic acid is produced every day, and were it not for the action of vegetation the amount produced would speedily set all animal life at rest. But our friends, the plants, decompose the carbonic acid by assimilating the carbon and setting free the oxygen which animals consume. Thus our atmosphere keeps its balance, so to speak. Nothing is lost in nature.