Please answer the following question: Given the following context:  In March 1916, Thomson exhibited four canvases with the OSA: In the Northland (at that time titled The Birches), Spring Ice, Moonlight and October (then titled The Hardwoods), all of which were painted over the winter of 1915–16. Sir Edmund Walker and Eric Brown of the National Gallery of Canada wanted to purchase In the Northland, but Montreal trustee Dr. Francis Shepherd convinced them to purchase Spring Ice instead. The reception of Thomson's paintings at this time was mixed. Margaret Fairbairn of the Toronto Daily Star wrote, "Mr. Tom Thomson's 'The Birches' and 'The Hardwoods' show a fondness for intense yellows and orange and strong blue, altogether a fearless use of violent colour which can scarcely be called pleasing, and yet which seems an exaggeration of a truthful feeling that time will temper." A more favourable take came from artist Wyly Grier in The Christian Science Monitor: Tom Thomson again reveals his capacity to be modern and remain individual. His early pictures—in which the quality of naivete had all the genuineness of the effort of the tyro and was not the counterfeit of it which is so much in evidence in the intensely rejuvenated works of the highly sophisticated—showed the faculty for affectionate and truthful record by a receptive eye and faithful hand; but his work today has reached higher levels of technical accomplishment. His Moonlight, Spring Ice and The Birches are among his best. In The Canadian Courier, painter Estelle Kerr also spoke positively, describing Thomson as "one of the most promising of Canadian painters who follows the impressionist movement and his work reveals himself to be a fine colourist, a clever technician, and a truthful interpreter of the north land in its various aspects".In 1916, Thomson left for Algonquin Park earlier than any previous year, evidenced by the many snow studies he produced at this time. In April or early May, MacCallum, Harris and his cousin Chester Harris joined Thomson at Cauchon Lake for a canoe trip. After MacCallum and Chester left,...  answer the following question:  What are the last names of the two individuals who were convinced to purchase Spring Ice?
A:
Walker