Thomas ' grandson inherited them from his father , and sold them at Sotheby 's in 1872 .
Although the sheets were trimmed at some time , obliterating the date from several , some still retain the date of 1807 , establishing the year of their completion .
Thomas ' grandson inherited some from his father , and sold some at Sotheby 's in 1872 .
Although the sheets were trimmed at some time , obliterating the date from several , some still retain the date of 1807 , establishing the year of their completion .