COMPARATOR. 229 COMPASS. tancc away from the concspomling division of the oilier scale, and this aniounl, as determined with the mieromelers, is their difference at that temperature. While the operation of comparing two scales does not seem particularly complicat- ed, nevertheless, in order to secure the desired high degree of precision, elaborate ])recaiitions are taken both in the construction anil manipula- tion of the apparatus. The temperature at which the scales arc compared is of course no un- important consideration, and in order that this should be uniform and easily determined, they are immersed in .a bath of liquid whose temper- ature can be maintained at some constant point. In the comparison of standards there must of course be an ultimate .standard to which all measures of length are referred, and this bar is considered correct at some one stated temper- ature. Copies of this are made and serve as secondary standards whose coefficient of expan- sion, minute errors, and other constants are known. Such comparisons are performed by the International Bureau of Weights and Pleasures at Paris, where comparators susceptible of the most accurate results and possessing all possible refinements are employed. (See Weights and Measures.) Similar Imt usually less precise ap- paratus is found also in the various national standard bureaus and physical laboratories. The Mcmoires du Bureau International defi Poids et Mesures (Paris) contain full and technical descriptions of the most accurate and approved apparatus and methods. COMPARETTI, kom'pa-ret'te, Domenico PiETRO Anto.mo (1835—). An Italian philolo- logist, born in Kome. He studied mathematics and the natural sciences, and in 1859 became professor of C4rcek in the University of Pisa. A few years later he accepted a similar position at Florence, and afterward went to Rome, where he conducted the lectures on Greek antiquities at the university. Aside from his Greek stiidies, he is distinguished as a scholar in Romance philology- and in the culture-history of the Mid- dle Ages. His most important works are: Safigi dei dialeiti greci deW Italia meridionale (1866) ; yirgilio nel medio ero (1872; Eng. trans. 1899) ; I'apiro ercolanese (1875) ; La eommissione ome- rica di Pisixtrnlo e il ciclo epico (1881). With d'Ancona he edited Canti c racronti del popolo ilaliaiio (1870-91); with others the Rivista di filologia e d'if:trii~ione elassica, and since 1884 has been editor also of the Museo italiano di anti- chita elasfiied. COMPARISON (OF. cowpnraisiin, Fr. com- paraison, from Lat. comparatio, from eoinparare, to compare). In grammar, and as applied to adjectives (q.v. ). that which marks the degree in which the quality is attributed to the object, as compared with other objects. There are three degrees of comparison. The positive in- dicates the quality generally, without com- parison; the comparative, a higher degree of the quality than is attributed to other things; and the superlative, the highest degree that is attributed to any of the things under considera- tion. Sometimes the positive is not regarded as a degree of comparison. There are two ways of expressing these degrees. (1) By an inflection or change of the word; as, hard, harder, hardest; happy, happier, happiest. This mode prevails almost exclusively in Greek and Latin. (2) By an additional word, as more hajipy, most happy. This may be called logical comparison, the other, grammatical. In French, with the exception of a few irregular adjectives, all adjectives follow the logical method. In English, the logical method is generally preferred when the gram- matical would produce a word difficult or hai-sli in the pronuncial ion. This is generally the case in English when the simple adjective is of more than one syllable ; but it is not always so. Thus, ciirnester, prudentcr, would make harsh com- binations ; not so politer, discrCeter, happier. The ditl'erence is, that in earnestcr, prudentcr, the accent being on the first syllable, two unac- cented syllables of discordant character are thrown together; in politer, discrceter, the un- accented syllables are separated ; and in happier, though they come together, they readily coalesce. Thus, the laws of euphony determine this point, as they do much else in language, Carlyle and Ruskin use many comparative and superlative forms that are not generally recognized. In gen- eral, it is only adjectives of quality that admit of comparison; and even adjectives of quality* cannot be compared when the quality does not admit of degrees ; as, a circular space, a gold ring, a luiiversal wish. Adverbs (q.v.) in Eng- lish are compared exactly like adjectives, logical comparison predominating. COMPASS (OF., Fr. compas, compass, from ML. conipassus, circle, from Lat. com-, together -- pas.nts, step, from pandere. to spread out). The most important instrument used in the nav- igation of a ship. It consists of a number of magnetic needles placed with their axes parallel ; a framework supporting the needles, and a circular disk marked in points and de- grees, called a compass-card ; the pivot on which the framework rests; and the compass-hoirl, containing the compass. This latter is, in tui'n, mounted on gimbals in a binnacle (q.v.) and further protected by a binnacle-cover. Com- passes are of two general types, dry and liquid. The best-known form of dry compass is that designed by Lord Kelvin (Sir William Thom- son, before his elevation to the peerage). It consists of a central boss and outer rim, both of aluminum connected by numerous radial silk threads. The magnets, eight or more in number, are held in parallelism by threads and supported by other threads from the rim. The latter has a paper cover marked in degrees and points. This compass is very light, and therefore will be very sensitive and yet not have too much throw as the ship moves. Furthermore, the weight, such as it is, being largely in the rim, will tend to check a tendency to liveliness. The dry compass is cheap and reasonably satisfactory in other respects, and is much used. In the United States JSTavy and in many ships of the merchant service a liquid compa.ss is used. The bowl is filled with alcohol and water. The com- pass-needles, in two or more bundles, are sealed in parallel tubes, which form the framework connecting the central boss to the rim. Both rim and boss are hollow, and, like the needle- tubes, are of white metal or aluminum alloy. The markings of the ordinary compass-card are painted upon the rim in degrees and points. The whole float, consisting of rim, boss, and magnetic tubes, is slightly heavier than the liquid, so that it rests very lightly upon an agate pivot-bearing in the boss, which is supported upon a pivot
