Fourteen lines, three kinds of glass, and a sting in the tail. Anne Finch's "Glass" begins as a hymn to human cleverness and ends as a joke with a moral edge. The speaker addresses "Man" directly and marvels at whatever "Inspiration" taught him to invent a material that divides "Light and Air". Windows admit "the useful Beams of Day" but shut out the wind. Mirrors return our own faces. Drinking glasses show us what we are about to swallow. Then the last line turns the transparency back on the drinker: if you take "th' Excess the Preacher warns to flee", then "Men at length as clearly spy through Thee."
The poem's pleasure lies in how it makes a familiar object strange. Glass is made by fire, since it is "extract[ed] from Embers", yet it looks like "Flakes of solid Ice". That paradox of heat producing something cold and clear gives the invention an air of magic. The wind becomes "subtil", a word that makes it seem almost intelligent, and the glass forces it to stay outside "without thy Shash", the old spelling of sash. The mirror is even better. Once "silver'd o'er", glass will "redouble all in place", and its candour is mildly comic, because it gives back "thy well or ill-complexion'd Face". A mirror flatters no one, and the poem enjoys saying so.
The third section is the cleverest. The "gloomy Bowl", an opaque drinking vessel, held the wine's "full excellence" in check by hiding it. Glass reverses this: "These shew the Body, whilst you taste the Soul." The line works on two levels. In wine-talk, the body is a drink's weight and colour and the soul is its spirit, so the eye and the tongue each get their share. But "body" and "soul" are also the large words of religion, and the line quietly lifts a tavern pleasure to a higher plane. "Its colour sparkles Motion" packs sight and movement into one phrase, as if the light in the wine were already dancing.
The form is carefully tuned to this movement. The lines are mostly iambic pentameter, but two of them stretch to twelve syllables: "Yet force, as subtil Winds, without thy Shash to stay" and "And give thee back thy well or ill-complexion'd Face". These longer lines come at the end of the window and mirror passages, and they have a lingering, expansive feel that suits a poem about what lets things pass through and what holds them back. The rhyme scheme gives the poem a quiet shape. Four couplets (Guide/divide, Day/stay, Device/Ice, place/Face) are followed by two triplets (Bowl/controul/Soul, then see/flee/Thee). That adds an extra line to each of the last two rhyme groups, so the poem feels as if it is gathering speed toward its ending. The final triplet needs its third rhyme, and that rhyme is "Thee", the word that turns the poem round. Capitalised nouns like "Light", "Air" and "Motion" give every object the dignity of a personification.
That final pun is what lifts the poem above a neat list of uses for glass. "To see through" someone means to detect their motives and their secrets, and wine is notorious for loosening tongues and dropping masks. So the drinker who has praised glass for its clarity risks becoming glass himself, with nothing hidden. The shift from the grand "O Man!" at the start to the pointed "Thee" at the end is a small drop in tone. It moves from admiration to a raised eyebrow, and the speaker cheerfully refuses to let humanity admire itself for long.
The poem is significant because it shows how much an ordinary object can hold. Window, mirror and wine glass are things any reader has handled, but Finch uses them to explore ideas of revelation, appearance and self-knowledge. She does it with wit instead of heavy preaching, and even the "Preacher" is brought in only as a passing reference. It is a compact lesson in how a poem can turn an object into an argument, and how a single well-placed word can change the direction of a whole piece.