Page:Popular Science Monthly Volume 1.djvu/392

378 glowing impression of the exact size and shape of the hollow flame. The moment the gas is extinguished, or the flame removed to the slightest distance from the solid, the effect ceases. This appearance, and the blue tinge which is said to be peculiar to the hydrogen-flame, are really due, according to Mr. Barrett, to the presence of sulphur, and so delicate is the reaction with this substance, that, without the greatest care in purifying the gas, and cleansing the surfaces with which, when burning, it is brought in contact, sufficient sulphur will be present to perceptibly color the flame. The least trace of phosphorus is also made apparent by the hydrogen-flame, by the production of a vivid-green light. When made to play upon the surface of clean tin, or some alloy of tin, a fine scarlet color is almost instantly produced, though the appearance is less vivid than with either sulphur or phosphorus.

Many gases also impart color to the hydrogen-flame; hydrochloric-acid gas giving a reddish-brown flame; ammonia gas a yellow flame, etc. Carbonic-acid gas, even in the smallest proportions, gives the flame a pale lilac tinge, the color being most marked at the base of the flame.

Mr. Barrett suggests that the delicacy of these various reactions makes it possible to turn them to valuable practical account, in the detection of the substances named. When, for example, the air of a room has become vitiated by the accumulation of an undue amount of carbonic acid gas, the hydrogen-flame, by means of suitable apparatus, will readily make the condition known. This practical side of the subject is now engaging Mr. Barrett's attention.

Recent Cave Explorations.—Some highly-important discoveries have lately been made in a cave near Luchon, France, by M. Piette, of the Geological Society. The soil of the casern consists of several layers—the lowermost ones being characterized by the bones of the reindeer, and by dressed flints like those of the grotto of Laugerie-basse. These layers enclose, in addition to human bones, a large fauna, and particularly a considerable quantity of carved bones and stones. Nowhere else has so great an accumulation of prehistoric works of art been found. The figures often cannot be recognized; still on the bones are seen some designs of considerable finish. M. Piette mentions, among other carvings, some that represent flocks of wild-goats, and herds of reindeer, the head of a rhinoceros, a wolf, horses, a lion's head with mane, etc. These valuable remains are buried in a black soil, filled with ashes. Near the surface of this layer the fauna is the same as it is below, but the carvings are very different from those underneath, and show a very marked decadence. While the lower ones reproduce Nature exactly, with extreme care and a certain minuteness of observation, the upper ones are fantastical and not after Nature, as well as ruder than the others. All the human bones, especially the bones of the skull, are reduced to small fragments, and all have notches and incisions more or less deep. This, M. Piette takes as an evidence of cannibalism. The topmost layer is hard and compact.

Relation of Death-rate to Temperature.—In a little work on the climate of Uckfield (England), Mr. J. Leeson Prince has the following concerning the influence of temperature on the death-rate:

"The mean annual temperature varies 5°.3, viz.: from 51°.93 in 1857, to 46°.62 in 1845, and although at first sight this difference may not appear considerable, yet it is sufficient to exert an enormous influence upon the general character of the seasons, the produce of the soil, and the health of the population. The registrar-general's interesting returns have fully established the important fact that there is a very intimate connection between temperature and mortality. Whenever the mean temperature falls to 45° or thereabouts, the number of deaths from diseases of the respiratory organs increases; and, should it fall below 40°, the death-rate from such diseases is still higher. When a period of intense cold prevails, so that the temperature scarcely rises above the freezing-point for two or three weeks, the number of deaths will be found to exceed what takes place during an epidemic of cholera or scarlet fever. But, when the mean temperature rises to 55°, there will be an increase in the number of deaths from diseases of the abdominal