This photograph was taken in April 1865, which would have been right around the time of President Lincoln’s assassination. You can see the unpaved roads of Maine Ave, SW. There are buildings in the foreground with the Capitol Building just visible in the background.
The Capitol Dome is nearly complete in the photo below. When Lincoln first took office, the Dome was under construction, at this point there were only small changes to be made before completion.

The view is quite different from today’s view. In a similar location, via Google Street View, the streets are obviously paved and the buildings have changed. You’d have to get really high up to see the Capitol Building now.

Maine Avenue ran parallel to and north of Maryland Ave, between 6th & 3rd Streets, on what is now the Air & Space Museum and the mall at that time.
In 1865 directory Somerville & Leitch were listed:
Brass founders and finishers between 4 ½ and 6/12 Maine Ave near the Columbian
Armory. Owners were Thomas Somerville and Robert Leitch. Their full page advertisement says:
“manufacturers of all the various articles used in the city
Plumbing, steam & gas-fitting
And
Locomotive and engine building business
Also
Brass castings of every description”
Later they may have made fire hydrants which would have made
sense.
http://firehydrant.org/pictures/somerville-leitch.html
Maine Avenue disappeared when they expanded the Mall. It was right below the then Botanic Gardens at the foot of the Capitol. Your current Maine Ave SW shot shows Arena Stage at Maine and M St SW.
I should have done this before I commented. Here is Thomas Somerville’s obit with his photograph!
Evening Star. (Washington, D.C.), 17 Oct. 1898. Chronicling
America: ( Lib. of Congress) http://chroniclingamerica.loc.gov/lccn/sn83045462/1898-10-17/ed-1/seq-16/
Looks like eventually Leitch went his own way sometime prior to 1881 and moved his business to D St. NW.
The Washington Times. (Washington, D.C.), 28 March 1895. Chronicling America: ( Lib. of Congress.) http://chroniclingamerica.loc.gov/lccn/sn87062244/1895-03-28/ed-1/seq-5/