5 82 THE POPULAR SCIENCE MONTHLY. 



natural science so highly valued by you and by me, as authorities in 

 this province. In order to be able to speak with authority concerning 

 any phenomena, one must possess a thorough critical knowledge of the 

 same. Authorities in the present case, therefore, are only such per- 

 sons as either possess mediumistic powers or, without claiming to be 

 bearers of such properties, are able to produce phenomena of the same 

 nature. As an authority I would therefore acknowledge Mr. Slade, 

 if he possessed scientific credibility, and also by all means Herr 

 Bellaihini, prestidigitateur in Berlin, who, as is well known, has de- 

 clared in favor of Mr. Slade, if I could premise in his case that he had 

 a conception of the scientific scope of this question. The only person 

 of whom this is true, and who, at the same time, has successfully imi- 

 tated many of the Slade experiments, is Dr. Christiani, assistant in the 

 Physiological Institute in Berlin. Dr. Christiani, however, declares his 

 experiments to be mere pieces of jugglery. Now, Herr Christiani is 

 certainly not able to imitate all of Mr. Slade's experiments ; but he 

 only professes to be an amateur in a field which Mr. Slade cultivates 

 professionally. 



I come to my second question : What influence may we concede to 

 outside authority upon our own knowledge f In the immensely pre- 

 ponderant majority of the things which we hold for certain, we all 

 follow the authority of other men ; we know only a proportionally 

 small number of facts from our own investigation. Yet all that we 

 owe to foreign authority passes for the more certain the more it agrees 

 with our observation. If a new fact is communicated to us, the inves- 

 tigation of which we are not ourselves in a position to control, then, 

 at least according to the principles hitherto authoritative in science, 

 two criteria must be satisfied, if we are to hold the same to be true : 

 First, it must be confirmed by a credible person, who is master of the 

 field concerned ; and, secondly, it must not contradict other established 

 facts. Now, you will probably urge here that this second criterion is 

 an exceedingly fluctuating one. Indeed, various spiritualistic authors 

 have not failed to adduce a multitude of instances from the history of 

 science, in which a fact was at first rejected as false or even impossible, 

 and was yet at last proved to be true. But I beg to call your atten- 

 tion to the fact that, in all these instances, the tertium comparationis 

 with the case before us consists simply and solely in the fact that 

 something was asserted by some scholars and denied by others. This 

 case still occurs of course repeatedly, and the controversy is always 

 decided in favor of those whose observations stand in contradiction 

 with no other established fact. Usually, indeed, the best passport 

 which a discoverer gives to his new observation consists precisely in 

 his indication of its agreement with other facts. I have looked in 

 vain through the whole history of science for a case in which a scien- 

 tific authority came forward with the assertion of having discovered a 

 new fact, at the same time adding to this assertion the assurance that 



