I like Bill's suggestion. It looks like the moustache in the fourth and eleventh images and the uniform of the ninth image on this page, and he's got two stars--
My guess: Major General Ambrose Burnside.
See: www.old-picture.com .
From there, Google " Ambrose Burnside ".
I stand by my opinions, however, that Burnside and Chamberlain were much younger when they achieved that rank. The absence of any other accoutrement makes me wonder if perhaps it is the uniform of a military school, or some such.
Yes Chamberlain was a young man when first a two star general.
But these photos are often made at the reunions of the union army.
Camberlain died in 1914 and this image looks quite elderly; this would not be possible as a real Brady image. Brady's Washington studio closed in 1881, New York in 1875, Putting this image before 1875, but his images were copied by Antony co. and reproduced for many years.
yep, it wasn't him ...
but if you do advance aging techniques,
AND flip the image of beck that i linked to
the person has the same nose, eyes, hair, face and moustache ...
too bad i can't do a seance at major general george sears greene's gravesite and ask him
... he is buried down the road from me ...