William A. Hammond, the dynamograph, and bogus neurologic testimony in old New York

April 25, 1870, court of General Sessions, New York City, Doctor William A. Hammond, neurologist and former Surgeon General of the United States Army, testified at the trial of his patient Daniel McFarland. McFarland had fatally wounded famous journalist Albert Richardson in November of 1869. Dr. Hammond said McFarland suffered from temporary insanity due to cerebral congestion from over use of the brain. Hammond told the jury he had, "devoted the last five years of his professional life exclusively to the study of the mind", and opined that the evidence of cerebral congestion was profound: McFarland's head was hot, and his carotid throbbed. The proof came from the test with the dynamograph machine: McFarland could not keep a pencil still to trace a straight line in the center of a moving piece of paper. The dynamograph, Dr. Hammond assured the jury, measured the power of a man over his will and thus provided "full and decided evidence" there can be no doubt that McFarland "could not control his will". What were the motivations behind the testimony of this famous expert witness? Did bogus neurologic testimony exist in old New York over a century before our time?