299• Typical studies are surveyed by Vemon (18, pp. 88-102) and Woodworth (19, pp. 340-367). •The influence of 'mental set,' experimentally demonstrated by Mohsin (13), has been emphasized by a number of writers, 6uch as Woodworth (19). Instead of regarding 'mental set' as a causative factor, a sort of hypostatized deus ex machina, however, it should be realized that 'mental set' is itself the result of immediately preceding stimulating conditions. * The corresponding figures for children over 12 years of age were: 'proletariat' 40 percent, 'better circles' 25 percent.