How would you describe the tone and theme in Walt Whitman's "To a Locomotive in Winter"?

The tone is one of celebration, as many of Walt Whitman's poems are.  He was a great lover of life, and appreciator of people, things, beauty, strength, progress and forward movement, and that shows  in his poem.  The entire thing is a beautiful and interesting description of the beauty and mighty power of a train, and a tone of respect, admiration, awe and celebration certainly come through as he hails and praises all of the parts and power of a locomotive.  The theme falls along these lines also--it is a theme of reverence for the strength and might of the train.  He wishes to incorporate its "madly-whistled laughter" and its "fierce-throated beauty" into his poem itself; he wants to have its power and force in his words, to barrel them forward with the same determination.

There is a definite and interesting theme of finding beauty in machines--this is something that poets before him really didn't focus on.  They tended to focus on nature, god, and the beauty that can be found outside, in birds, clouds, etc.  Whitman, in a bold move, instead praises and touts the beauty of a man-made and very noticable machine that cuts across nature's landscape.  To relish a machine was not a very "romantic" thing to write a poem about, but, the theme of finding admiration and power in such a machine is strong in Whitman's poem.  He shows his unique talent of finding what is admirable in things that often, other people overlook, and that was a major anthem in all of his poems.  I hope that helped; good luck!