He was the son of the Kendal physician James Ainslie.
[1] Educated at Hawkshead Grammar School and then Pembroke College, Cambridge (where he graduated Senior Wrangler and was second in the Smith Prize), he became a fellow of Pembroke in 1782, and a Fellow of the Royal College of Physicians in 1795.
In 1785 he married Agnes Ford of Monk Coniston (an estate near Coniston Water in the English Lake District) in the church at Colton.
The couple owned Ford Lodge at Grizedale and planted many thousands of larch trees in the valley and on the surrounding hills and moorland which effectively started Grizedale Forest.
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