[April, 
236 On Space of Four Dimensions. 
be explained through the generalised conception of space 
and the platonic hypothesis of projection, coincided with 
so-called spiritualistic phenomena. Cautiously, however, I 
said 
“ To those of my readers who are inclined to see in 
spiritualistic phenomena an empirical confirmation of 
those phenomena above deduced in regard to their 
theoretical possibility, I beg to observe that from the 
point of view of idealism there must first be given 
a precise definition and criticism of objective reality. 
Indeed, if everything perceivable is a conception pro- 
duced in us by unknown causes, the distinguishing 
characteristic of the objective reality from the subjective 
reality (phantasma) cannot be sought in nature, but 
only in accidental attributes of that process producing 
conceptions. If causes unknown to us produce 
simultaneously in several individuals the same con- 
ception, only subject to those distinctions which 
depend upon differences in the position of the ob- 
servers, we refer such conception to a real objeCt 
outside of us ; this conception not taking place, we 
refer that conception to causes within us, and call it 
hallucination. 
“ Now, whether the spiritualistic phenomena belong 
to the first or to the second category of these concep- 
tions, I do not venture to decide, so far never having 
witnessed such phenomena. On the other hand, I 
do not possess, with regard to men like Crookes, 
Wallace, and others, such an exalted opinion of my 
own intellect:, as to believe that I myself, under 
similar conditions, should not be subject to the same 
impressions.” (Written in August, 1877.) 
This supposition received, four months after my writing it 
down, a full confirmation by the above-mentioned experi- 
ments with the American, Mr. Henry Slade. In making 
them I was intent upon giving full consideration to the 
above-cited distinction between a subjective phantasma and 
an objective faCt. The four knots in the above-mentioned 
cord, with the seal unbroken, this day still lie before me ; 
I can send this cord to any man for examination ; I might 
send it by turn to all the learned societies of the world, so 
as to convince them that not a subjective phantasma is here 
in question but an objective and lasting effect produced in the 
material world, which no human intelligence with the con- 
ceptions of space so far current is able to explain. 
If, nevertheless, the foundation of this faCt, deduced by 
