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):
Camp at Rappahannock Station
Wednesday September 2d 1863
Dear Wife
I today received your letter from La Noraye of 29th inst and was very glad to find that you were all Safe back home again – You can scarce imagine the pleasure that dear Julia & Harry’s letter gave to me I could almost fancy Julia saying “Us went into bathe” and Harry’s “quawl about” – their little expressions are very full of pleasant association – Oh if this war business was only over and we could only get back – I hear there are 17 Regiments on the list to get Recruits at Philad and as yet only 9 have rec’d any – As we are the 17th it will be long before any come to us – We had a sort of intimation given to us that we might soon expect an attack from the Reb’s Tis said that Stewart has lately had all his Cavalry horses shod &c &c – and as we are really weak it is very possible that some move might be made as last year towards our flanks. We have about 1000 men on the other side of the Bridge with a pontoon bridge to be taken up and a rail road bridge to be destroyed if we move and then for about 3 miles We shall be within easy shelling distance – but I don’t apprehend anything. Don’t speak to me of my gift to you of $300 – My beloved you haven’t yet got over your maidenly individualities – idiosyncrasies I should call them – I don’t know what better I can do with anything I have than to put it in the way of ministering to your Comfort or pleasure – I think that you the children & dear Uncle are pretty much all I have left…
Citation: Alexander Biddle (1819-1899), autograph letter signed to Julia Williams Rush Biddle, 2 September 1863. Rush IV:30:35
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thanks!!…