SPECIFIC GKAVITY. 422 SPECTACLES. as in the figure the specific gravity would be .8642. The glass cylinder carries a small ther- mometer, and the temperature should be ad- justed to about 15°. The method is extremely convenient to three places of decimals. The fourth requires many corrections. (E) Hydrometer. A long hollow glass cylin- der or 'stem' weighted at one end by a bulb con- taining shot or mercury so that it will float upright in a liquid. The stem is graduated and the specific gravity is given by the mark to which it sinks, read through the liquid. The graduations are sometimes in specific gravity or density, but often according to established arbi- trary scales, those of Beaume and Twaddell being best known. Instruments are made of diil'erent styles for milk, spirits, oil, acids, etc. See Hydbometeb. I HTDBOMETEB. APPARATUS FOH METHOD OF BALANCING COLTJMNy. (F) Balancing CoLrMN.s. A tube such as that shown is supported vertically in two jars containing two liquids. These are drawn up into the tubes by suction on the tube at the top, which is then closed. The height of the liquids in the tubes above their surfaces in the tumbler are inversely as their densities. If the liquids do not mix a simple inverted U tube may be used, one liquid being poured into each arm. If tubes less than half an inch in diameter are used the liquids should be drawn up only a little, heights measured, then as far as possible, and the ratio of the increase in lengths of the columns taken. (G) The specific gravity of a solid lighter than ■water is found by either the hydrostatic or Jolly's balance, a weiglit being attached sufficient to sink it. This weight should hang under water throughout. III. Specific Gravity of Gases. Bunsen's Method. The rate of effusion of a gas, i.e. the volume which escapes per second through a very small opening, is for a given opening and dif- ference of pressure inside and out, inversely as the square root of its density. Near the top of a long vertical glass tube is a partition consisting of a disk of platinum pierced by a hole about .0005 inch in diameter. Above this the tube is closed by a ground stopper. The tube is filled with gas and plunged into a deep bath containing mercury and adjusted until a glass float carried by the mercury stands at a fixed level. The stopper is removed and the time required for the float to rise to another fixed level as the mercury drives out the gas is meas- ured. The experiment is then repeated in ex- actly the same manner with the standard gas. Tile ratio of the times observed is the square of the ratio of the densities, i.e. the specific gravity of the unknown gas referred to the standard gas. See iIoLEcri.ES — JIolecvlar Weights. For tables of density and specific gravity, con- sult Smithsoitiaii Physical Tables (Washington, 1896) . , Methods of determining the specific grav- ity of a substance will be foimd in any standard text-book on physics. SPECIFIC HEAT. See Heat. SPECIFIC LEGACY. See Legacy. SPECIFIC PERFORMANCE. A technical legal term emplnyed to denote the equitable doc- trine and rules under Avhich a court may compel a party who has refused to perform his part of an agreement to carry it out according to its terms. In an action at law for the breach of a contract the only relief possible is damages, but as money is not always an adequate compensa- tion for the loss which may be suffered, the courts of equity will in certain cases decree a specific or actual performance of the terms of the contract. It lies in the discretion of the court whether or not to grant this relief, but precedents must be followed as a guide. In gen- eral, to obtain a decree of specific performance the plaintiff must satisfy the court that the remedy at law is entirely inadequate ; that there was a valid, fair, and reasonable contract be- tween the parties; and that he has done nothing inequitable on his part. It is a general rule to grant specific performance of contracts for the conveyance of real estate. It is only in excep- tional cases that the relief will be granted in cases of contracts to convey personal property, and then only when the article is unique in its character and practically unobtainable elsewhere, such as a rare picture which could not be dupli- cated. In a few eases specific performance of a contract to do some act, such as build a struc- ture, will be decreed. For example, where a rail- road agreed to build an ornamental bridge over a private roadway in consideration of the right of way through a man's premises, the court de- creed that the company should construct the bridge according to the terms of their contract. Consult Fry, On Specific Performance. See also Contract, and authorities there referred to. SPECTACLED BEAR (so called from the marking on the face). The small bear of the northern Andes. See Beak. SPECTACLES (Lat. spectaculum, show, from spectare, to behold, from specere, to see; con- nected with Gk. (TKiTTTtaBai, sJ^eptesthai, to look, Skt. spas, to see, OHG. spehOn, Ger. spiihen, to
