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SURETY, SURETYSHIP 175 SURGERY failure of the principal, is liable to pay the debt and damages; a bondsman, a bail. A surety of good behavior is a recognizance or obligation to the com- monwealth entered into by a person with one or more sureties before some com- petent judge of record, whereby the parties acknowledge themselves to be in- debted to the commonwealth in a speci- fied amount, with condition to be void if the defendant shall demean and behave himself well, either generally or spe- cially, for the time therein limited. It in- cludes surety for the peace and some- thing more. A justice may bind over all night-walkers, such as keep suspicious company, or are reported to be pilferers or robbers, common drunkards, cheats, idle vagabonds, and other persons whose misbehavior may reasonably bring them within the general words of the statute as persons not of good fame. A surety of the peace is the acknowledgement of a bond to the commonwealth, taken by a competent judge of record, for keeping the peace. SURFACE, in mathematics, the bound- ary of a solid, having two dimensions, length and breadth. It may be con- ceived to be generated by the motion of a straight or curved line, just as a curve is generated by the motion of a point. Of all surfaces, the most important are those of the second order, which are in- tersected by a straight line in at most two points, and whose curve of section by a plane is a curve of the second order. Hyperboloids, ellipsoids, paraboloids, spheres, cones, and cylinders, and also the limiting case of two planes, are in- cluded among the so-called quadric sur- faces. SURFACE TENSION, in liquids, that property in virtue of which a liquid sur- face behaves as if it were a stretched elastic membrane — say a sheet of india- rubber. The idea is due to Segner (1751); but it was Young who in 1805 first applied it successfully to the ex- planation of various physical phenom- ena, such as those of capillarity. The whole subject was subsequently devel- oped in its complete mathematical form by Laplace and Gauss. Pure water has the highest surface tension of any or- dinary liquid except mercury. If a little alcohol be dropped on the water, the sur- face tension will be diminished there. The more powerful surface tension over the pure water will show its superiority by pulling the alcohol over the whole sur- face till the surface is reduced to uni- formity, and equilibrium produced. Drops of liquid, free from all but their own molecular forces, assume spherical forms. this being the only shape consistent with equilibrium under the influence of equal surface tension at all parts of the curved surface. Ripples on the surface of any liquid progress because of the action of surface tension, which gives rise to an inward pressure on any convex surface. In cohesion figures we have some very exquisite phenomena. These are pro- duced by dropping a dark-colored liquid into a transparent liquid of slightly smaller density. Ordinary ink dropped into water will serve the purpose very well, though better effects are obtained with a solution of permanganate of potash. As the drop meets the water surface, the action of the surface ten- sion pulls the under surface of the drop outward, and transforms the drop into a vortex ring which slowly sinks through the clear fluid. As it so sinks it breaks up into smaller rings and shoots out fan- tastic ramifications of rare beauty. Ul- timately, of course, under the influence of diffusion, the vortex motion decays and the dark liquid mixes with the clear liquid. SURF DUCK, or SURF SCOTER, a species of duck {Oidemia perspicillata) , about the size of a mallard, rarely seen on the British coasts, but frequently on the coasts of Labrador, Hudson Bay, and other parts of North America. SURGEON, one who practises sur- gery; in a more limited sense, one who cures diseases or injuries of the body by operating manually upon the patient. In a more general sense, one whose occupa- tion is to treat diseases or injuries by medical appliances, whether internal or external. In ichthyology, a popular name for any species of the genus Acanthurus, from the sharp, erectile, lancet-shaped spine with which each side of the tail is armed. In the early stages of their growth these fish are so different from the fully-developed individuals, that for some time the young fish were placed in a separate genus, Acromirus. Surgeon-general, in the United States Army the chief of the medical depart- ment. In the British Army a surgeon ranking next below the chief of the med- ical department. SURGERY, manual intervention, me- diate and immediate, in all lesions or malformations of the human body. It was already an art when medicine proper was but a phase of superstition. The earliest notices of it occur among the Egyptians, who, as we find represented on obelisk and in temple, practiced inci- sions, scarifications, probably even am-