Expression, child of soul! I fondly trace
Thy strong enchantments, when the poet's lyre,
The painter's pencil catch thy sacred fire,
And beauty wakes for thee her touching grace-
But from this frighted glance thy form avert
When horrors check thy tear, thy struggling sigh,
When frenzy rolls in thy impassion'd eye,
Or guilt sits heavy on thy lab'ring heart-
Nor ever let my shudd'ring fancy bear
The wasting groan, or view the pallid look
Of him[A] the Muses lov'd-when hope forsook
His spirit, vainly to the Muses dear!
For charm'd with heav'nly song, this bleeding breast,
Mourns the blest power of verse could give despair no rest.-

Helen Maria Williams

http://www.poemhunter.com/poem/sonnet-to-expression/