Alexander Biddle was a member of the prominent Philadelphia Biddle family and was married to Julia Williams Rush, the granddaughter of Dr. Benjamin Rush. Biddle served with the 121st Pennsylvania Volunteer Infantry, beginning in September 1862. Starting out as a major, he would participate in Fredericksburg and Gettysburg, among other engagements, and would leave the service as a lieutenant colonel. (He was commissioned, but never mustered, as colonel) 
Transcript (excerpt):
Head Qrs 121st Regiment P.V.
Camp near Belle Plains Virg.
February 15th 1863
Dear Julia
Yesterday Saturday we broke up our quarters at the new camp near WOChurch and came where we now are about two miles from Belle plains on the edge of a ravine which runs nearly N E into Potomac Creek. On the Easterly Side of this ravine on the slopes of the hill the camps of our Division will be pitched. Ours is already made the men were last night in their New quarters – After arriving at the camp I rode over to Rush’s Cavalry as I told you and returned – towards nightfall we got orders for a mounted officer to report at Division Hd Qrs today at 9 Oclock During the night it rained almost without ceasing but did not make us uncomfortable until morning when it began to drop through our canvas roof and trickle down our walls my boots which had been prepared the night before had each about a wine glass full of water in them and it was so wet out of doors that we cooked our breakfast before our own little fire – I rode in the rain to Genl Doubleday’s who has also just moved his quarters and had a long talk with him about out Regimental Officers suitable for aids &c. He told me he thought the two important points to be taken were Chattanooga and a point about 20 miles from Edisto S.C. by taking these two places the Confederacy would be cut in pieces and unable to unite any great force any where. Ask Uncle to look at it on the map…
Citation: Alexander Biddle (1819-1899), autograph letters signed to Julia Williams Rush Biddle.15 February 1863. Rush IV:30:28