[6] The two eldest brothers worked in the Clydebank shipyard of J&G Thomson & Co Ltd, soon to be known as John Brown & Company, Alexander qualified as a member of the Institution of Naval Architects, and was the top prizeman in Britain in his final year.
[2][3][4] Today, this is recognised by the term ‘air conditioning.’ In 1901 he and his brothers set up their own firm, Thermotank, based in Glasgow with works coming next to the Clyde at Govan in 1908, and later with branches and agencies overseas.
On his passing the Liverpool Journal of Commerce wrote:"Like all great engineers, he had the gift of imagination, which enabled him to approach problems from new angles, and avoided the conventional ruts of ordinary practice.
He was tenacious and untiring ,in his pursuit of perfection in the installations and systems which he designed;, and the high standard of comfort, so far as heating and ventilation is concerned on our latest luxury liners, is largely due to Mr. Stewart's devotion to the problems associated therewith.
"[3]Alexander remained unmarried and shared the family home of his brother Frederick and sisters at 8 Lancaster Crescent, Glasgow and at Craigrownie Castle,[8] Cove, overlooking the Firth of Clyde, until his passing in 1933.