There's something obvious missing here, unless I've missed it in the posts as well. I know Joe said it early on, but I get the impression Genie didn't understand. I hope this helps.

If you don't type the phrase in quotes, the search engine will look for the individual words and not the phrase.

You can type in: "let us smile"
NOT: let us smile
It's best not to use upper case letters

You can type: "let us smile" "your umbrella"
and the search will find documents containing one of the prases or the other or both.

If you type "let us smile" AND "your umbrella"
it will find documents containing both phrases.

Often when searches are unsuccessful, I go back and check the quotes and find something just a bit wrong. It may be "let us all smile" or "your big umbrella." I searched for let and us and smile and your and umbrella and found Let a Smile be Your Umbrella.

I found this while trying to find your poem:

I. Prologue. A Sense of Humor
By Vachel Lindsay [Nicholas Vachel Lindsay, Illinois Artist. 1879-1931.]

No man should stand before the moon
To make sweet song thereon,
With dandified importance,
His sense of humor gone.

Nay, let us don the motley cap,
The jester's chastened mien,
If we would woo that looking-glass
And see what should be seen.

O mirror on fair Heaven's wall,
We find there what we bring.
So, let us smile in honest part
And deck our souls and sing.

Yea, by the chastened jest alone
Will ghosts and terrors pass,
And fays, or suchlike friendly things,
Throw kisses through the glass.