successive years from 1905-1911: 85, 87, 106, 124, 112, 100 and 156 days (O’Connor, 17). With the increase of coal consumption has come an increase of smoky days. Dr. Benner tells me that the per cent. of daylight (as chemically determined) in Pittsburgh was reduced for last November about 32%, for December 23%, January 36% and February 44% as compared with the town of Sewickley which is only about 12 miles distant. There can then be no doubt that smoke lessens the amount of sunshine. Smoke likewise is directly related to the production of moisture, mist, clouds, rain or fogs, because it supplies some of the solid particles which may serve to aid in the formation of suspended drops of water. Rain drops are often formed around a solid nucleus. Without solid particles of dust in the atmosphere there would probably be much less mist, rain and dew (4). We would, therefore, infer on merely _a priori_ grounds that smoke contributes to the production of fogs. That this is so seems to be shown by actual investigation. An investigation conducted by the Meteorological Council in 1901-1903 indicated that 20% of the fogs in London were smoke-induced, (4, 21)--artificially induced and therefore preventable fogs. Most suggestive, as showing that smoke is partly responsible for the existence of fogs, are the fog and smoke statistics gathered in London during the last 30 years, as shown in Table IV (applicable to the winter months only). The number of days of fog have been reduced nearly 300% and the hours of bright sunshine have increased nearly 100% during this 30-year period (10). TABLE IV. Date Days of Fog Hours of bright sunshine 1883-1892 29.9% 55.6% 1892-1901 20.7% 70.1% 1901-1910 10.6% 93.5% Likewise in Westminster the number of days of fog averaged 27 per year for the lustrum 1902-1906, and 17 per year for the period 1907-1911. The improvement shown above is due, in large part, to the increased use of gas and electricity and to better stoking (Kershaw, Russell). On the other hand, if we turn to Pittsburgh where the amount of smoke has been on the increase in recent years, we find that the number of days of fog increased from an average of 22.6 per year for the first five year period to 50.2 for the second five year period, 1907-1911.