Page:The American Cyclopædia (1879) Volume XI.djvu/417

 MEECY Therefore very little reliance can be placed on the accounts some telescopists have given of marks supposed to be seen on the planet's sur- face, nor can his rotation period be regarded as fully determined from features so unsatis- factorily observed. Even the estimates of his diameter can scarcely be regarded as altogether trustworthy; but it is not probable that it greatly exceeds or falls short of 3,000 mjles. His volume is about -j-ff ^ of the earth's, and his density greater than hers in about the pro- portion of 10 to 9 ; so that his mass is about Tinhr ^ * ne earth's. He travels round the sun in rather less than three of our months, his mean sidereal revolution being completed in 87*9693 days. His mean synodical revolution, or the mean interval between his successive returns to inferior conjunction, amounts to 115'877 days ; so that he passes through all his phases (from inferior conjunction to maximum elongation west of the sun, thence to superior conjunction through maximum elongation west of the sun, to inferior conjunction again) more than three times in the course of each year. But as he is only visible for a short time after sunset on three or four evenings when his elon- gation is easterly, and for a short time before sunrise on three or four mornings when his elongation is westerly, he is not often seen. In America he might be seen oftener than in England, however, as the twilight skies are seldom free from light mist in the latter country. It is commonly said that Mercury rotates on his axis in 24h. 5m. 28s. ; but great doubt rests on the determination of this element, for the reason above mentioned. Mercury, travelling within the earth's orbit, sometimes transits (or passes across) the face of the sun. The first phenome- non of this sort ever observed took place in No- vember, 1631, and was witnessed by Gassendi. A transit of Mercury is not so important in astronomy as a transit of Venus, because the nearness of Mercury to the sun prevents his having a measurable relative parallax ; in other words, whereas Venus, seen from two distant stations on the earth during any moment of her transit, is projected at two spots measur- ably separated from each other on the sun's disk, this is not the case with Mercury. ' The observation of Mercury in transit, however, is interesting as illustrating the phenomena which occur during a transit of Venus. The forma- tion of the "black drop," a small black liga- ment which at the moment of contact seems to connect the disk of the planet with the dark space outside the solar disk, is very manifest in the case of Mercury, though, owing to his disk being so much smaller than that of Venus, and his motions more rapid, the phenomena are not so readily studied. Transits of Mer- cury take place at intervals of 13, 7, 10, 3, 10, and 3 years. MERCY, Sisters of. or Order of Onr Lady of Mercy, a religious order founded in Dublin by Miss Catharine .McAuley in 1830. Miss Mc- Auley was born in Gormanstown castle, near MEEGANSER 405 Dublin, Sept. 29, 1787, and died Nov. 13, 1841. Her parents, who were Eoman Cath- olics, died while she was a child, and she was brought up without any definite religious faith. But she became a Eoman Catholic, and devoted herself and her large fortune to the service of the poor. She induced several la- dies to join her, purchased a house in Dublin, and there in 1827 opened an asylum for desti- tute young women and a free school for poor children. Soon afterward she and her com- panions underwent a regular novitiate in a convent of Presentation nuns, and in 1831 as- sumed there the habit and took the vows of the new order. The rules first drawn up were sanctioned by the archbishop of Dublin, Jan. 23, 1834 ; but subsequently the rule of St. Au- gustine, modified to suit the active duties of the sisterhood, was adopted by them, approved by Gregory XVI. in 1835, and formally con- firmed by him in 1840. The sisters of mercy spread rapidly over Great Britain and her colo- nies. The first American house was estab- lished, at St. John's, Newfoundland, in 1842, and the first in the United States at Pittsburgh in 1843. In 1874 the order possessed houses of protection for servant girls, schools, asy- lums, and hospitals in all the New England, middle, and western states, including Califor- nia and Washington territory, and in nearly all the southern states. The sisters of mercy have in view, besides other charities, the vis- itation of the sick and prisoners, the instruc- tion of poor girls, and the protection of virtu- ous women in distress. Wherever their means permit they found "houses of mercy," where destitute girls of good character are cared for until employment can be found for them. They are subject to the bishops, and have no general superior, the communities of each dio- cese in the United States forming one body governed by a common superior, who is elect- ed by the professed choir sisters, and confirmed by the bishop. The sisterhood is divided into two classes, choir sisters and lay sisters. The former are employed about the ordinary ob- jects of the order, and the latter about the do- mestic avocations of the convent and such oth- er duties as may be assigned to them. Candi- dates for membership of either class undergo a preliminary " postulancy " for six months ; at the end of that time they assume the white veil and become novices. The novitiate lasts two years. The vows, which are taken for life, bind the members to poverty, chastity, obedience, and the service of the poor, sick, and ignorant. The habit of the order is a black robe with long loose sleeves, a white coif, and a white or black veil. In the streets a bonnet of black crape is worn instead of the coif and veil. MERGANSER, a name applied to most of the saw-billed ducks, of the subfamily mergince, of which the goosander, the largest species, has been described under that title. The bill is very Slender, narrow, compressed, ending in