May my book have the good fortune to contribute, however feebly, towards removing the prejudices which keep away so many likely experimenters from these studies and researches. These prejudices are manifold: there is the fear of ridicule, the religious scruple, the delusive dread of nervous or mental disease, the terror of an unknown world peopled with strange, mysterious beings. But time will dispel all this, and I believe that a day will come, when these facts—well studied, well observed—will change our conceptions of things in a way little dreamt of to-day. The sphere of ‘Psychical Science’ is unmeasurable. A few pioneers only are exploring therein to-day; when the land has been tilled and cultivated it will yield, I am sure, a wonderful crop—the harvest will surpass the dreams of imagination. But let those who, thanks to a scientific education, are particularly well qualified to undertake these studies, cease to consider them unworthy of their attention. In holding themselves aloof they commit a mistake which they will bitterly regret some day. Allowing even that the first experimenter may be guilty of mistakes, there will always remain something out of the facts which they have observed. Mistakes are unavoidable in the _début_ of a new science: the methods are uncertain, and the novelty of the phenomena makes their analysis difficult; time, labour in common, and experience will remedy these inevitable inconveniences. It would be very easy to give examples of the delay which scientific prejudice has brought to bear upon scientific progress. This criticism has already been very frequently and wittily made. Even those men, whose discoveries have placed them at the head of the intellectual movement of their generation, are not altogether free from blame, yielding too often to the deplorable tendency of converting natural laws into dogmas. They commit the same fault they object to in theologians. Man has a wonderful aptitude for laying hold of his neighbours’ faults and remaining blind to his own, and probably it will be so for a long time to come. I would like to see science rid itself for good and all of this theological habit of mind.