Question

what is the meaning of phrase "stream of glass"
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Answer 1

in these lines, we get more beautiful landscape imagery: a breeze stirring the grass and the river flowing like glass (that's a simile if you're scoring at home). The speaker emphasizes all the wonderful things that the bird is missing out on.

Answer 2

"When the wind stirs soft through the springing grass,

And the river flows like a stream of glass "

• More magnificent landscape imagery can be found in these lines, with a breeze stirring the grass and a river that is flowing like glass

• The speaker focuses on all the great things that the bird is missing out on. Our little birdie can't take advantage of the pleasant wind or the flowing river if it's in a cage.