165. But although, with a view to convince the skeptical, spirits will occasionally give manifestations when the vision or muscular control of the medium is nullified, it is more difficult for them to operate in this way; moreover, it is more difficult for some spirits than for others. 166. Those spirits by whom I obtained my test manifestations were interested in my success. Others have refused to aid me in like manner. One who has assisted me with much zeal, has communicated that he would work my apparatus when arranged for a test; but, that as it caused much more exertion, and, of course, retardation, he advised that the test arrangement should not be interposed when it could be avoided. 167.[7]The table, at this stage of my inquiry, was not more than thirty inches in length. I had improved the construction in the following way: 168. Two of the legs were furnished with castors, through holes duly bored. Through perforations in the other two legs a rod was introduced, serving as an axle to two wheels of about five inches diameter. One of these wheels was grooved, so as to carry a band which extended around the pulley of the disk. Hence, pushing the table nine inches horizontally by the necessary rotation of the supporting wheels, caused the disk to make a complete revolution. It was while the table was of the size above mentioned, that I first saw the violent action to which they might be subjected without any corresponding or commensurate visible cause. The hand of the medium being laid on the table at about half-way between the centre and the nearest edge, it moved as if it were animated, jumping like a restive horse. 169. Having my apparatus thus prepared, a medium sat at my table, the screen intercepting her view of the disk. No manifestation took place through the disk, though other indications of the presence of spirits were given. Hence, inducing the medium to sit at an ordinary table, I inquired if any change could be made which would enable them to communicate through my apparatus? The reply through the alphabetic card was, “Let the medium see the letters.” At first it struck me that this would make the experiment abortive, as it would remove the condition by which alone independency of interference by the medium was secured. However, it soon occurred that by means of a metallic plate, made quite true, and some brass balls, like billiard balls, with which I was provided, I could neutralize the power of the medium to move the table, so that she could not influence the selection of the letters, though permitted to see them.