The article in Blackwood’s Magazine to which Meade refers in this letter to his son, John Sergeant, was written by Arthur Fremantle, a British officer who was present at Gettysburg with Lee’s army. You can read the entire article here.

I have read the article in Blackwood, which is tolerably fair for a “secesh” Englishman. The general officer referred to as being cheered was your humble servant, and I was at that time riding down the line to the left, for the purpose of ordering an attack; but it was so late and the distance to the enemy’s line so great, that by the time the troops were in motion the day was at an end.

Lee’s report has just been published. Considering all things, it is pretty fair, in some places a little too much of what the lawyers call the suppressio veri. Still, I am willing to leave to history the fact, which he plainly admits, that after the battle of Gettysburg he had to retreat continuously till he reached the south bank of the Rappahannock, from whence he had started to destroy my army and accomplish other valuable results.

Meade’s correspondence taken from The Life and Letters of George Gordon Meade, Major-General United States Army, Vol. 2, (New York: Charles Scribner’s Sons, 1913), p. 153. Available via Google Books.