The obvious difference is the lack of locking bolt notches on the periphery of the 1889 cylinder. I am sure there are other locking improvements but I can't tell you what. I just look for the lack of the notches to ID it as an 1889. Hope this helps.
The first 5000 model 1889s were sold to the U.S. Navy. Other smaller numbers were bought by the gov't for the navy, army, coast guard and national guard units. When Colt updated the action in 1892, the government decided to send the 1889s back to be changed to the newer design. Most of the internals are the same on both guns so the update was not too invasive. Most of the Navy 1889s were updated so finding one in it's original condition is difficult. Later, some of the same guns went back to Colt and other places to be updated to the 1894/5 design. Only a few guns missed this upgrade. The first update involved changing the cylinder and adding a bolt. In the later modification, an addition was made to prevent the revolver from firing unless the cylinder was completely closed. The book by Robert Best on these guns is probably the best single source of information on them. You can find his book for sale on Amazon and other places. A good read and tons of information!
thank you gentlemen. i see what you mean by the lack of notches on the cylinder. that makes it easy to identify. wison's book says there were 31,000 1889 Navys made until 1894. so were the ones made from 1892.1893 and 1894 basically the same guns as THE NEW NAVY MODEL?