Of the Several Graces Used in Music:
The first and most principle grace, necessary to be learned, is the trill or shake; that is, to move or shake your voice distinctly on one syllable the distance of either a whole tone or a semitone, always beginning with the note or half note above, as in the following.
The method of learning this trill, is first to move slow, then faster by degrees; and, by diligent practice, you will soon gain the perfection of it.
The trill ought to be used on all descending pricked notes, and always before a close; also on all descending sharped notes, and on all descending semitones; but (in psalmody) none shorter than crotchets.
In songs and instrumental music the trill is greatly used, and generally has (tr.) set over the notes which are to be shaked, for the better inspection of the performers. And, as this most delightful grace is equally ornamental in psalmody, I will add another example, and place (tr.) also over the notes you are to shake; but, as the trill is mostly in use in the trebles and tenors in church music, an example in the treble cliff may suffice.
There is another Grace used in Music, called the Grace of Transition; that is, to slur or break a Note, to sweeten the Roughness of a Leap, &c. And is greatly used in singing Solo Parts in Anthems, &c. But is not so much required in Chorus’s; but I will here give an Example somewhat of this Kind, shewing where it is to be used in several Parts in Psalmody’
John Arnold, The Compleat Psalmodist : Or, The Organist’s, Parish-Clerk’s and Psalm-Singer’s Companion, Fifth edition (1741; repr., London: R. Brown, 1761).