A person's mental attitude has an almost unbelievable effect on his powers, both physical and psychological. The British psychiatrist, J.A. Hadfield, gives a striking illustration of this fact in his booklet, The Psychology of Power. "I asked three people," he wrote, "to submit themselves to test the effect of mental suggestion on their strength, which was measured by gripping a dynamometer." They were to grip the dynamometer with all their strength under three different sets of conditions. First he tested them under normal conditions. The average grip was 101 pounds. Then he tested them after he had hypnotized them and told them that they were very weak. Their average grip this time was only 29 pounds! In the third test Dr. Hadfield told them under hypnosis that they were very strong. The average grip jumped to 142 pounds.