Page:Popular Science Monthly Volume 41.djvu/149

Rh of weather conditions and phenomena in other parts of the kingdom indicates that there were other observers in England who corresponded with Merle. A comet was seen in the second week of September, 1343, appearing about sunset. Our author called it "ardens draco," or burning dragon, but did not seem terrified by it. He merely remarked that it was a sign of dry weather. In the same year, on the 28th of March, is entered a notice of an earthquake so violent that the stones of the chimneys in certain parts of Lindsey were thrown down. The motion lasted while one might say the angelic salutation, which was about half as long then as it is now. The mention of stones falling in the stone chimneys "lapides in caminis lapideis" is interesting, as it proves the fallacy of the belief that chimneys are a late invention, and that the English of those times were so barbarous that the smoke was got rid of by means of a hole in the roof. The recovery of the journal is due to a mention of it by Dr. Plot, of the Royal Society, in 1685, as being in the Bodleian Library. It was looked for and found.

Drops of Fog.—Advantage was taken by Mr. John Aitken, during a visit to the Righi, of the opportunities that were afforded there for investigating the water particles in clouds. With an instrument the author has invented those particles were distinctly seen showering down, and the number falling on the micrometer was easily counted. The number was observed to vary greatly from time to time. The greatest rate actually counted was sixty drops per square millimetre in thirty seconds, but for a few seconds the rate was much quicker. The maximum rate named gives twelve thousand drops per square centimetre per minute, or seventy-seven thousand four hundred drops per square inch per minute. The drops are so extremely small that they rapidly evaporate, more than two or three being seldom visible at the same time on one square of the micrometer. The denser the cloud the quicker was the rate of fall, and as the cloud thinned away the drops fell at longer intervals, and they diminished in size at the same time. It was frequently observed when the mountain-top was in clouds, particularly if they were not very dense overhead, that the surfaces of all exposed objects were dry—not only the stones on the ground, which might have received heat from the earth, but also wooden seats, posts, etc.—and if wetted they soon dried. And while everything was dry, the fog-counter showed that fine rain-drops were falling in immense numbers, and the air, on testing, was found to be saturated. A few observations were therefore made to explain the apparent contradiction of surfaces remaining dry while exposed to a continued shower of fine rain and surrounded by saturated air. The explanation was found to be, simply, radiant heat. A considerable amount of heat, as also of light, was found to penetrate the clouds, notwithstanding their density. This radiant heat is absorbed by all exposed surfaces and heats them, while they in turn heat the air in contact with them, and the fine drops of water are either evaporated in this hot layer of air or after they come in contact with the heated surfaces. Other observations made on Mount Pilatus pointed to the same conclusion. All large objects, such as seats, posts, etc., were dry in cloud when there was any radiation; while small objects, such as pins, fine threads, etc., were covered with beads of water. The large surfaces being more heated by radiation than small ones, when surrounded by air, these surfaces evaporate the drops falling on them, while the small ones, being kept cool by the passing air, are unable to keep themselves free. The observations made with the fog-counter point to the conclusion that the density or thickness of a cloud depends more on the number of water particles than on the number of dust particles in it.

Mortality and Morbidity by Professions.—M. Jacques Bertillon recently communicated to the French Society of Public Medicine a table of mortality by professions, compiled from official documents of the city of Paris from 1885 to 1889. This is the first table of the kind that has been made in France. Other tables have been made in England by Mr. William Farr and by Mr. Ogle, compiled from the returns of census years, and in Switzerland by M. Kummer for the years 1879 to 1882. On a comparison of the results of these four tables, made with special reference to the relative number for