Page:The American Cyclopædia (1879) Volume I.djvu/137

 ADHESION Cenis tunnel. In the so-called atomizer a cur- rent of air is used to divide water into a fine spray. In the Giffard injector a blast of steam is used to carry water by its adhesion to it into the boiler against its own pressure. The adhe- sion of air to water is further illustrated by the friction of a strong wind on its surface, which not only pushes it forward, but creates the waves. If oil is spread over the water, the air finds a surface for which it has little adhesion, and glides easily over it. This is the cause of the quieting influence of oil upon ocean waves, of which advantage has occasionally been taken in a storm by vessels having oil on board ; the oil will spread at once over a large surface. The peculiar motions of camphor on water, phosphorus on mercury, &c., belong to the same class ofphenomena ; it is the elective affinity of the vapors of these volatile sub- stances for the liquid on which they float, which is the cause of a strong and unequal evaporation at the points in contact, the evolv- ing gas or vapor pushing the floating solid on- ward by its mechanical reaction. When the water is touched with a substance containing the merest trace of oil or grease, the motion of the camphor stops at once, as the water be- comes then at once covered with a very thin but strongly adhering oil film, which has no affinity for the vapor of the camphor. A similar action is seen as soon as mercury is covered with a film of phosphorus ; removing this film with the edge of a knife, the motion recommences at once, and is visible in the dark. The mutual adhesion of liquids and gases is also illustrated by the floating of watery particles in the atmosphere, as is seen in clouds and fogs. Watery vapor, present in the air in an invisible condition, becomes visible as soon as condensation commences, when a kind of fine water dust is formed, identical with the spray of large cataracts, where it originates by mechanical means. These watery particles are kept floating simply by their adhesion to the air, the total surface being very large com- pared with the total weight; but when the particles, by contact and mutual adhesion, form larger bodies, the total surface diminishes in proportion to the weight, while finally their gravitation becomes greater than their adhe- sion, and they fall down like rain. This fall- ing down of water dust not only takes place in a vacuum, but even a trifling diminution in the atmospheric pressure will cause it when the amount of watery vapor in the air is large, as seen in the fact that rain is usually preceded by a descent of the mercurial column of the barometer. A descent of temperature is also a cause of this condensation of watery vapor, as it diminishes the capacity of the air for holding it. This adhesion theory makes the hypothesis of De Saussure quite unnecessary. This savant imagined that the particles of watery vapor were supported in the clouds by being hollow, with a vacuum inside, and thus, -being lighter than the same volume of air, they were sup- ADIPOCERE 117 ported like a balloon. He was strengthened in this notion by the microscopic illusion which often causes solid small spheres to ap- pear as if hollow. Still such hollow spheres are occasionally seen like microscopic soap bubbles, but they have air inside, are heavier than the air, and are only supported by adhe- sion. 6. Gases to gases. The interpenetration of gases being very great, it is impossible to keep their surfaces distinct ; there must con- sequently be much adhesion and friction be- tween them. Direct experiment with two gases cannot well be made, but observation demonstrates this great adhesion and friction. So one small jet of air in a wide tube will cause a rush of air to follow; the exhaust steam blown upward in the locomotive flue causes the air to rush out with it, and so creates the draft necessary to keep up a sufficient heat. This adhesion of gases plays no doubt a most important part in the actions of the atmosphere in the economy of nature. ADIGE (anc. Athesis-; Ger. EtecK), a river of the Tyrol and N". Italy, rises in the Swiss Alps, and flows E., S., S. E., and again E. about 220 m. to the Adriatic, S. of Chioggia. On its banks are the towns of Trent and Roveredo in the Tyrol, and the fortresses of Verona and Legnago in Venetia. ADIPOCERE (Lat. adeps, fat, and cera, wax, from its fatty origin and waxy consistency), a white, solid, non-putrescible substance, into which human bodies are sometimes converted after burial. If the dead body be left exposed to the air at a moderate temperature, it under- goes the process of putrefaction, and is rapidly decomposed with the evolution of offensive and putrefactive gases. If buried in closed coffins with a limited supply of air, or in a tolerably dry soil, the process is somewhat modified; the putrescent character of the changes is less marked, the offensive effluvia are much less abundantly developed or are absorbed by the soil, and the body slowly decomposes, losing its original form and structure, and finally crumbling away to powder, leaving only the bones, which remain for a long time after the remainder of the body has become unrecog- nizable. But occasionally it has been found that bodies disinterred after the lapse of many years have not undergone either of these changes, but on the contrary have been con- verted into a white,, solid, and very heavy sub- stance, of firm consistency, retaining the ori- ginal size and contour of the frame, so that the features may still be distinguishable, and even the natural markings and texture of the skin distinctly apparent. This substance is adipo- cere. It does not putrefy, but has evidently remained, unchanged for a long time while buried, and after disinterment continues with but slight alteration. After exposure to the air it simply becomes lighter in weight, drier and more granular, owing to the evaporation of the water which it contained ; so that a body which has undergone this conversion may be