does “negative” here means that the doctors deny presence of a supernatural force or they accepted it?
Attempts to expose the phenomena were made from time to time. In February, 1851, Dr. Austin Flint, Dr. Charles A. Lee, and Dr. C. B. Coventry of the University of Buffalo, published a statement [Capron "Modern Spiritualism, etc.," pp. 310-31.] showing to their own satisfaction that the sounds occurring in the presence of the Fox sisters were caused by the snapping of knee joints. It called forth a characteristic reply in the Press from Mrs. Fish and Margaret Fox, addressed to the three doctors: As we do not feel willing to rest under the imputation of being impostors, we are very willing to undergo a proper and decent examination, provided we can select three male and three female friends who shall be present on the occasion. We can assure the public that there is no one more anxious than ourselves to discover the origin of these mysterious manifestations. If they can be explained on "anatomical" or "physiological" principles, it is due to the world that the investigation be made, and that the "humbug" be exposed. As there seems to be much interest manifested by the public on that subject, we would suggest that as early an investigation as is convenient would be acceptable to the undersigned. Ann L. Fish. Margaretta Fox.
The investigation was held, but the results were negative. In an appended note to the doctors' report in the New York Tribune, the editor (Horace Greeley) observes:
The doctors, as has already appeared in our columns, commenced with the assumption that the origin of the "rapping" sounds must be physical, and their primary cause the volition of the ladies aforesaid—in short, that these ladies were "The Rochester impostors." They appear, therefore, in the above statement, as the prosecutors of an impeachment, and ought to have selected other persons as judges and reporters of the trial . It is quite probable that we shall have another version of the matter.