5. That ozone is in greatest quantity in spring, less in summer, diminishes in autumn, and is least in winter.
6. It is most frequently detected on rainy days, and during great atmospheric disturbances.
7. That atmospheric electricity is apparently the great generator of ozone.
The subject is one of great interest in its bearings on health, and opens a wide field of scientific research, as may be inferred from the opinion expressed by the Vienna Congress, which is that “the existing methods of determining the amount of ozone in the atmosphere are insufficient, and the Congress therefore recommends investigations for the discovery of better methods.”
Mr. Lowe has published the valuable weather warnings tabulated on page [94], which are interesting as showing from a given number of observations the value of each phenomenon:—
| No. of observations. | Followed in 24 hours by | ||
| DEW. | Fine. | Rain. | |
| Dew profuse | 241 | 196 | 43 |
| Dew from 1st April to 30th Sept. | 185 | 161 | 24 |
| Dew from 1st Oct. to 30th March | 56 | 37 | 19 |
| CLOUDS. | |||
| White stratus in the valley | 229 | 201 | 28 |
| Coloured clouds at sunset | 35 | 26 | 9 |
| SUN. | |||
| Solar halos | 204 | 133 | 71 |
| Sun red and shorn of rays | 34 | 31 | 3 |
| Mock suns | 35 | 19 | 6 |
| Sun shone through thin cirro-stratus | 13 | 6 | 7 |
| Sun pale and sparkling | 51 | 27 | 24 |
| FROST. | |||
| White frost | 73 | 59 | 14 |
| MOON. | |||
| Lunar halos | 102 | 51 | 51 |
| Mock moons | 9 | 7 | 2 |
| Lunar burr | 64 | 47 | 17 |
| Moon shining dimly | 18 | 12 | 6 |
| Moon rose of a red colour | 8 | 7 | 1 |
| STARS. | |||
| Falling stars abundant | 85 | 65 | 20 |
| Stars bright | 83 | 64 | 19 |
| Stars dim | 54 | 32 | 22 |
| Stars scintillated | 14 | 12 | 2 |
| AURORA. | |||
| Aurora borealis | 76 | 49 | 27 |
| ANIMALS. | |||
| Bats flying about in the evening | 61 | 45 | 16 |
| Toads in the evening | 17 | 12 | 5 |
| Landrails clamorous | 14 | 13 | 1 |
| Ducks and geese noisy | 10 | 7 | 3 |
| Spiders hanging on webs in the evening | 8 | 5 | 3 |
| Fish rise in the lake | 15 | 9 | 6 |
| SMOKE. | |||
| Smoke rising perpendicularly | 6 | 5 | 1 |
Among the animals whose movements give weather warnings few are more trustworthy than the leech. The reader may verify this by placing one in a broad glass bottle, tied over with perforated leather, or bladder. If placed in a northern aspect, the leech will be found to behave in the following manner:—
1. On the approach of fine or frosty weather, according to the season, it will be found curled up at the bottom. 2. On the approach of rain, snow, or wind, it will rise excitedly to the surface. 3. Thunder will cause it to be much agitated, and to leave the water entirely.
Periods.—M. Köppen states, as the result of his examination into the chances of a change of weather, that the weather has a decided tendency to preserve its character. Thus, at Brussels, if it has rained for nine or ten days successively, the next day will be wet also in four cases out of five; and the chance of a change decreases with the length of time for which the weather from which the change is to take place has lasted.
In the case of temperature for five-day periods, the same principle holds good;[[17]] for if a cold five-day period sets in after warm weather, we can bet two to one that the next such period will be cold too; but if the cold has lasted for two months, we can bet nearly eight to one that the first five days of the next month will be cold too. The chance of change is, however, greater for the five-day periods than for single days. Similar results follow for the months, but here again the chance of change shows an increase.