Page:Popular Science Monthly Volume 30.djvu/590

570 between the action of diffused daylight sufficient to view pictures and of direct sunlight is at least forty times as great, and in summer probably four hundred times. Hence a picture which would fade in ten years in sunlight might be preserved for something like twelve hundred years in a yellow light. The acidity of drawing-paper should be corrected by a wash of a dilute solution of borax; and in no case ought any paste, gum, or glue, to be placed at the back of a drawing for the purpose of mounting it.

The Mineral Springs of Europe.—Dr. J. Burney Yeo has made a classification of the mineral springs of Europe into groups according to the composition of their waters. The first group includes the simple thermal waters, or "indifferent" springs, the temperature of which is above 80° Fahr. The waters are chiefly used in baths, and, when administered internally, it is simply for getting the purifying solvent influence that might be obtained from drinking pure hot water. They are efficacious in chronic rheumatism, chronic gouty inflammation of the joints, sciatica and other forms of neuralgia; hysterical and hyperæsthetic states of the nervous system; old, painful wounds and cicatrices, and cases of loss of muscular power when not dependent on diseases of the nervous centers. Some of the most popular springs fall under the head of "common salt waters." Their strength varies, and it is customary to fortify them or dilute them, artificially, according as they may need. Used in baths, they stimulate the peripheral vessels and nerves, and promote capillary circulation. They improve the tone and nutrition of the skin, and indirectly stimulate tissue-change. Internally they act as stimulants and indirectly as tonics to the organs of digestion and assimilation; but in persons with highly sensitive mucous membranes they may cause irritation and discomfort, especially if given in too large doses. They are employed in baths in cases of hypersensitivencss of the skin; in some forms of retarded convalescence from acute disease; in scrofulous and inflammatory enlargement of joints; and in chronic hypertrophies of certain organs. Internally they are beneficial in cases of atonic dyspepsia and chronic gastric catarrh, and in those low states of health which are often contracted by prolonged residence in tropical climates. The alkaline waters are characterized by the presence of considerable proportions of carbonate of soda and free carbonic acid in varying amounts, and are exemplified at Vichy. Some of them also contain common salt, when they are classed as muriated alkaline waters, and some, of both simple and muriated springs, are hot and some cold. Many of the springs of this class are found to be most valuable curative agents. The waters are all taken internally, and are used in baths, but not very largely. They are applicable to the treatment of a great number of chronic maladies. In moderate doses they are solvent and purifying, correct acidity, promote tissue-change, and possess active diuretic properties. If taken too largely, they depress the heart's action and cause emaciation. They are given in cases of acid dyspepsia; in gouty constitutions; in cases of renal calculous disorders and gravel; in diabetes; and in cases of torpid liver, with tendency to gall-stones, in constitutions which would not bear the stronger aperient waters. They are of service in the treatment of chronic catarrh of the bronchial and other mucous membranes. The waters containing common salt are more tonic and stimulating than the simple alkaline waters. The group of the sulphated waters includes all the best-known aperient waters, which owe their peculiar qualities to the presence of soda and magnesia, singly or combined. Some of the springs contain also carbonate of soda and chloride of sodium, which add greatly to their remedial value. This has led to the subdivision of the group into the simple sulphated or bitter waters—Friedrichshall, Pullna, and Hunyadi—and alkaline sulphated waters—ex-emplified in Carlsbad, Marienbad, Franzensbad, and Tarasp. The iron or chalybeate waters are the tonic waters. They are valuable in proportion to their purity—that is, to the absence of other solid ingredients—and in proportion, usually, to the amount of free carbonic acid that they contain. A sixth group comprises the numerous and well-known sulphur-springs, both hot and cold, which are freely used for baths. The celebrated Pyrenean spas are nearly all hot