This particular form of chair known as a 'Cockpen chair', became popular from the second half of the 18th and is particularly associated with Scotland.
Initially it was the overwhelming interest in chinoiserie promoted by William Chambers' Designs of Chinese Buildings (1757) and Charles Over's Ornamental Architecture in the Gothic, Chinese and Modern Taste (1758), soon followed by designs for Chinese lattice-style chair backs with straight legs by the celebrated London cabinet-maker, Thomas Chippendale, published in The Gentleman and Cabinet Maker's Director (1762), plates XXV and XXVII, that made such chairs fashionable. Contemporary Edinburgh cabinet-makers James Stark, Alexander Peter (the latter subscribed to Chippendale's Director), and Young, Hamilton and Trotter included similar designs in their repertoire.
In the 18th century these chairs were referred to as 'in the Chinese taste' or possibly 'diamond backs' but by the end of the 19th century, the cabinet-making firm of Wheelers of Arncroach of Fife, who made a significant amount of furniture for Robert Lorimer, had renamed it the 'T-chair', after the manner in which the back was constructed (Sebastian Pryke, 'Cockpen Quest', Country Life, 29 April 1993, pp. 80-81).
The name 'cockpen' entered the vernacular in the 19th century and seems to originate from Cockpen Church, Midlothian, where similar chairs were made for the family pew of the Earls of Dalhousie. Early examples can be found in Arniston House, Midlothian and in the collection of the Dukes of Hamilton at Lennoxlove, East Lothian (Ralph Edwards, The Dictionary of English Furniture, vol. I, 1954, p.285, fig.188). Related pairs of Scottish cockpen chairs sold Sotheby's, New York, 19-20 April 2001, lot 559 ($13,200 including premium) and 12 October 2005, lot 365 ($18,000 including premium).