Here is the letter from his father after Hill told him he wanted to go into the army:

Immediately on seeing your letter, I consulted those whom I thought most likely to inform me on the best plan for a young man to pursue who went into the army. What is most recommended is to go to a foreign academy for about two years, where strict attention to the several studies necessary to cut any figure in the profession must be attended to. By great favour, a commission may be purchased before you go abroad, with leave of absence, whereby you may stand a chance of creeping a little forward towards rank, the same as if you was with the regiment. This, to be sure, is a more expensive plan than I can well afford; but as I have not a doubt but you will make every proper return, I will exert myself to put it, or something of the sort, into execution (provided you continue in your present resolution); for I much dread the idea of a young man starting in any line of life without his being determined to use his utmost endeavours to advance in it, which I am well assured no one can in the military line, any more than any other, without a proper previous education. It is true a commission may be purchased for a few hundreds: but what a miserable situation for a young man of spirit , with scarce any thing but three and sixpence per day, to saunter about from town to town, unless he has a good prospect of advancing from it.

Sidney, Life of Hill, pp.9-10.