The most important and interesting series of facts, however, connected with ozone are those established by the researches of M. Houzeau, who states:— 1. That country air contains an odorous oxidizing substance, with the power of bleaching blue litmus, without previously reddening it, of destroying bad smells, and of bluing iodized red litmus. 2. That this substance is ozone. 3. That the amount of ozone in the air at different times and places is variable, but this is at most 1/700,000 of its volume, or 1 volume of ozone in 700,000 of air. 4. That ozone is found much more frequently in the country than in towns. 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:—