Page:Popular Science Monthly Volume 18.djvu/735

Rh mildest winters and the warmest summers, must be looked for where the land approaches the thirty-fifth parallel, at the southern points of Spain, Sicily, and Crete. The highest known mean in Europe is at Catania, 65°, the temperature of January being there 51°, and that of August 81°. Gibraltar enjoys a warmer temperature in January, 54°, nearly corresponding with the temperature of Cairo. The January of Catania is like that of the end of April, the January of Gibraltar like that of the first half of May, in Berlin. These extreme southern points suffer, however, occasionally from frost and snow. Snow fell on the African coast in 1845 and 1850, and in the latter year a temperature below the freezing-point was observed as far south as the Sahara; and the Nile is said to have been frozen in the year 859. So it is safe to assume that no place in Europe is secure from snow and frost.

A New Theory of Chemical Affinity.—M. Berthelot has endeavored, in his recently published "Essai de Mécanique Chimique fondée sur la Thermochimie," to connect the laws of chemistry and the theory of the unity of physical forces. He believes that he has discovered a direct relation between chemical affinity and the capacity of different bodies in combining to throw off heat. Thus hydrogen burns in oxygen, liberating enormous quantities of heat; the affinity of the two bodies is known to be strong. The same is the case with phosphorus and oxygen. But nitrogen and hydrogen, instead of liberating heat when they combine, absorb it. Their affinity for each other is feeble. Again, when two bodies combine in different proportions, forming different compounds, it is always the combination in which the most heat is liberated that tends to form. More heat is liberated in the formation of water than of the binoxide of hydrogen, and it is water that is naturally formed when the bodies burn together. This law of chemical compositions and decompositions has been termed by M. Berthelot the principle of maximum work, and is enunciated by him thus: Every chemical change accomplished without intervention of a foreign energy (heat, electricity, light) tends to the production of the body or system of bodies which liberates heat. This principle throws light on a multitude of facts hitherto unexplained. M. Berthelot indicates many applications of his principle. Acetic acid, combining with soda, produces a certain amount of heat, and forms acetate of soda; hydrochloric acid, combining with soda, liberates more heat, and forms chloride of sodium. If, now, we apply hydrochloric acid to the acetate of soda, chloride of sodium will be formed, with the production of an amount of heat just equal to the difference between the heat of formation of acetate of soda and that of chloride of sodium; but the converse will not take place when acetic acid is mixed with chloride of sodium. Combinations which are formed with much liberation of heat are very stable; those in which heat is not liberated are unstable. Chloride of sodium will resist a white heat without decomposing, while chloride of nitrogen, in the formation of which heat is absorbed, will decompose and explode spontaneously. This fact leads to another remark: that, in accordance with the law of maximum work, all explosive bodies are bodies that produce heat in being decomposed.

Diseases of Miners.—Dr. Paul Fabre, of Commentry, France, has made a particular study of the diseases of miners. He has found that diseases, the character of which is largely governed by certain accessory circumstances, are prevalent among workmen who labor in damp or wet galleries. No morbid symptom is developed among those who work in a gallery which is simply damp and of a temperature of not more than 58°. But if cold water falls upon them, or if they have to put their legs in water, they become subject to lumbago, sciatica, to indefinite pains in their limbs, and often to a real rheumatism. The rheumatism is generally subacute, sometimes chronic, and most often localized in a single joint—generally that of the left knee, on which the pick-men and heavers rest in working. In galleries which are saturated with moisture and where the temperature exceeds 77° to 86°, the workmen are soon overcome with an extreme lassitude; they get hot, they gasp for breath, the sweat rolls down their bodies, and they are obliged to stop working and rest for a while in a cooler spot, A rapid