Hymns.--The first hymn mentioned in the annals of Christianity was that sung by the angels at the Birth of our Lord, from which we have the _Gloria in Excelsis_, and the second was that sung by our Lord and His Apostles immediately after the Last Supper in the upper room, known as the _Hallel_. In early times anything sung to the praise of God was called a hymn. Afterwards the use of the term became more restricted. Pliny shows that in the year 62 the Christians instituted a custom of meeting together before sunrise to sing hymns of praise. Melody only was used, not harmony, and the tunes employed were, doubtless, of Jewish character. Originally all music of the Christian Church was almost entirely vocal. In the Third and Fourth Centuries the Christian Religion began to grow largely in the number of its followers, in wealth and position; magnificent churches were built under Constantine the Emperor, and then it came to pass that choirs were instituted definitely by the Council of Laodicea, A.D. 367. For two centuries the music of the Church deteriorated. In the Sixth Century Gregory the Great instituted many reforms, so that the credit of reviving real congregational singing belonged to him. (See GREGORIAN MUSIC.) The {142} connection of religion with music is shown by the fact that nearly every great revival of religion has been accompanied by a great outburst of song. Beginning with the Reformation, the form of hymn, called _chorale_, originated in the reformed Church of Germany and largely with Martin Luther. The most popular part in congregational singing was the singing of hymns and there have been three successive styles in hymn-tunes. The first was the diatonic; the second the florid (from 1730 to 1840), and the third the modern style (from 1840 to the present time). This modern style is in some respects a return to the old style of the Sixteenth and Seventeenth Centuries, with this distinction, that the harmonies instead of being pure diatonic are more chromatic and less plain. (See MUSIC, also ORGANS.) Hypothetical Form.--(See BAPTISM, CONDITIONAL.) I Ichthus.--The Greek word for FISH (which see). I. H. S.--The first three letters of the Greek word for JESUS, and equivalent to the English letters J. E. S. They are largely used in Church decorations as symbols of the Holy Name. Immersion.--The dipping into the water of recipients of Holy Baptism. For the relative importance of _Immersion_ and _Affusion_, see article on AFFUSION. Immovable Feasts.--Those Feasts of the Church which always occur on the same date such as {143} Christmas Day, Feast of the Epiphany, etc. As some of the Feasts, such as Ascension Day, Whitsun Day, etc., are movable depending on the time Easter is kept. Tables and Rules for the Movable and Immovable Feasts are set forth in the Prayer Book for convenience and to avoid confusion. (See CHRISTIAN YEAR, also FEASTS AND GOSPEL.)