Like two trains passing in the night

What is source of:
"Like two trains passing in the night"

I haven't heard that. I have heard "two ships passing in the night." From the archives:

It's from Longfellow's poem: The Theologian's Tale: Elizabeth, from the collection titled The Theologian's Tale.

"Ships that pass in the night, and speak each other in passing;
Only a signal shown and a distant voice in the darkness;
So on the ocean of life we pass and speak one another,
Only a look and a voice; then darkness again and a silence."