Count Rumford contended the phlogiston theory of heat not to explain experimentally observed phenomena.
Count Rumford contended that the phlogiston theory of heat did not explain experimentally observed phenomena.
Count Rumford contended the phlogiston theory of heat not to explain experimentally observed phenomena.
Count Rumford contended that the phlogiston theory of heat did not explain experimentally observed phenomena.
The verb "contend," when used in the cognitive sense (i.e. to assert), idiomatically takes a "that"-clause, never an infinitive.