A Little Help On 1840's(?)cover Please!

I got this cover awhile ago and it has been festering in my mind what the 10 is for?I am not very knowlegible on stamps/covers...BUT I do love them and collect Erie,PA. Cancels,covers,etc.But the 10 got me,It can't be the cost can it? Any info will be greatly appreciated! The Erie cancel is obviously a light strike.Thank's ALL&HAPPY HUNTING!

10 is the rate marking. The Erie Post Office rated this letter at 10 cents (in this case collected from the recipient), based on the rates in effect July 1, 1845-June 29, 1851, charging 10 cents for half-ounce letters ging over 300 miles.

10 cent rate for distance over 300 miles from Erie to Philly circa 1845-51

The addressee of the cover, Herman Cope, Esq., of Philadelphia, was a man regarded in the highest esteem. Most of us could only hope to have that sort of a reputation throughout our lifetime:

Thank You John Becker,SPQR&wt1( wt1,Thank's for extra info!! )i wasn't sure if that was cost or what,Obviously it the rate..I kinda thought that( as I have others ) but was NOT sure so I needed the knowledge of the Stamp Community!! And as ALWAYS the community came through,Again THANK YOU!!

The most time-efficient and cost-efficient way to build any collection is to have the correct tools. A 1-day visit to the APRL in Bellefonte would supply you with photocopies from countless postal history references to get you up to speed on Erie's stampless markings, fancy handstamp markings, machine cancels, railroad & waterway cancels, RFD markings, precancels, postmasters, rates, etc., not to mention seeing copies of studies on the postal history of similar-sized towns. A little investment in the knowledge already set-down by those who went before us will pay you huge dividends.

Along this line, a good starting point for stampless would be Thomas Mazza's "Postal Markings on Stampless Mail from Erie County, Pennsylvania" from 1993. It shows reported markings for the period and also lists out postmaster names and compensation information. Additional markings and examples will have turned up since then but it's still a good reference.