Rhine and his colleagues attempted to address these criticisms through new experiments described in the book "Extrasensory Perception After Sixty Years" (1940). Rhine described three experiments the Pearce-Pratt experiment, the Pratt-Woodruff experiment and the Ownbey-Zirkle series which he believed demonstrated ESP. However, C. E. M. Hansel wrote "it is now known that each experiment contained serious flaws that escaped notice in the examination made by the authors of "Extra-Sensory Perception After Sixty Years"". Joseph Gaither Pratt was the co-experimenter in the Pearce-Pratt and Pratt-Woodruff experiments at the Duke campus. Hansel visited the campus where the experiments took place and discovered the results could have originated through the use of a trick so could not regarded as supplying evidence for ESP.