Is the poem lesson by James r Lowell a imabic pentameter?

No, the poem "The Lesson" by James Russell Lowell is not written in iambic pentameter. The poem is written in trochaic tetrameter, which consists of four trochees per line. A trochee is a metrical foot consisting of one stressed syllable followed by one unstressed syllable. Here is the first stanza of the poem, divided into trochaic tetrameter:

Once, against the forest's edge,

As the evening sun was down,

In the twilighted air I heard

The whisper of a gown.