This is a nifty cover sent from Newburyport, Massachusetts(a nice strike of the CDS and grid!), to Machias(a pretty good receiving CDS), Maine, on September 23, 1887. It was addressed to a Ms. Dunan(?), in care of a Captain Charles Hosmer, U.S. Coast Survey!
To continue, the U.S. Coast Survey, is the United States' chartmaker! From 1807, it was under the control of the Department of the Navy. From 1832, its responsibilities were switched over to civilians!
Moving on, the mail arrived in Machias on September 25, 1887. The brown, 2-Cent, "Washington," is in very fine condition! The envelope is also in quite good condition, with some minor staining at its top. The back flap is intact. Noted imperfections aside, this is a neat piece of mail connected to a captain for the U.S. Coast Survey, Charles Hosmer!