Fort Summer. -The three works, Franklin, Ripley, and Alexander, have been combined into one powerful work of the name.

Forts Mansfield, Simmons, and Bayard have been built between Summer and ReNumbers

Fort Reno (formerly Pennsylvania) has been extensively modified, bomb-proofs added, and the powerful battery in advance constructed. Connecting the works mentioned (from Summer to Reno) are Batteries Benson and Bailey, and several others, and lines of covered way rifle-pits.

Fort Kearny, a powerful work, has been built between Reno and De Russy, as also Batteries Russell, Smead, Terrill and covered way rifle-pits.

Fort De Russy. -Modified and improved. Between it and Fort Stevens, the Batteries Kingsbury and Sill and lines of rifle-pits have been constructed.

Fort Stevens (formerly Massachusetts) has been extensively enlarged and improved. Between it and Fort Slucom three new batteries and lines of rifle-pits have been constructed.

Fort Slocum, originally one of the weakest, has become one of teh largest and most powerful works on the line . Between Forts Bunker Hill and Saratoga, Saratoga and Thayer, Thayer and Lincoln, numerous batteries for field guns have been built and constructed and supported by lines of rifle-pits.

Fort Lincoln has had additional bomb-proofs built. The spur or ridge between it and the Eastern Branch has been occupied by the powerful Battery Jameson, and by rifle-pits arranged as covered ways.

Fort Mahan has been strengthened by the construction of bastionets, for flanking.

Fort Meigs has been extensively enlarged. All other works not mentioned have, with scarce an exception, received considerable improvement and modification.

On nine different points having the most extensive command, 100-pounder Parrott guns have been mounted so as to bring every part of the ground in front of our line under their fire. Two new batteries, Parrott and Kemble, were built expressly for such guns, and their special function is, with Battery Cameron, to sweep the heights across the Potomac between the Chain Bridge and Fort C. F. Smith,.

For the defense of the Potomac, the two water batteries (Battery Rodgers and Fort Foote) have been constructed. They are essentially finished, and are receiving their armament. The latter is a powerful inclosed work, and the most elaborate in its internal arrangements of all the defenses of Washington.

The works described is either finished or brought to a state of efficiency; still a system of works of this character demands constant watchfulness and expenditure to keep it up, and there are yet some works that require overhauling, and all of them ought to have their scarps either rivetted or sloped and sodded. Fort Ward, in particular, a very important work, was built in great haste, and demands almost complete rebuilding.

It is a maxim among railroad men that "when the cars can go over the road it is half done. " Turn-outs have to be made, depots, sotre-houses, officers, &c., have to be built. The track must be ballasted, tunnels, cuts, and embarkments enlarged, and, finally, a second track must be laid. It is quite likely that this maxim will apply