10 
spencer’s ‘‘first principles.” 
Jan., 1889. 
which disappeared in the water. He could follow it for a 
time. He saw it change its condition from a lump to a 
powder. But when it went into the water it ceased to affect 
his sense of sight. Yet the fact that salt could be obtained 
from the water again leads him to think that it was in 
existence all the time. And he ascribes to the salt in its 
invisible state the change in weight of the water and the 
change in its taste. His belief in the continuity of existence 
of the salt, in its identity, rests on a postulate which for 
shortness we may term the continuity or identity postulate. 
Let us, for the sake of clearness, consider another example of 
the use of the same postulate. 
Suppose that I am with a man whom I know, in a room 
with a door leading into another empty room, and suppose 
that shortly before my friend has gone into the other room 
out of my sight,and has now returned again. I do not suppose 
that he went out of existence in his absence ; I believe that 
lie was in the other room, preserving meanwhile his identity. 
I mav have snoken to him while he was out of sight, and mav 
have received an answer, and this affection of another sense 
than sight I ascribe to him. I base my belief in his con¬ 
tinuity on the same postulate as that on which the 
experimenter bases his belief in the continuity of the salt. 
I have not a sufficient knowledge of philosophy to put the 
postulate in its proper form, but a consideration of cases in 
which it would not or might not apply may at least give us a 
working form of statement. If, during the weighing 
experiment, somebody had been observed introducing fresh 
salt on to the balance, we could no longer assert identity of 
the initial and final salt. Or if, in the second example, my 
friend had a twin brother in the neighbourhood, and if the 
adjoining room communicated with the street, I might not be 
sure of the identity of the friend underlying the two 
appearances. Perhaps, then, we may guard against such cases 
by the statement that “ if a thing affects us in the same way as 
a thing has previously affected us, and if we have reason to 
suppose that no fresh thing has come in from the outside, 
then the two affections arise from the same thing.” 
Secondly, with our experimenter, we assume that the 
weights used in the counterpoise preserve a constant 
weight. Mr. Spencer seems to think that this assumption 
is ultimate or fundamental. But let us examine the 
assumption a little more closely. To begin with, we 
assume continuity of existence of weight. We have only 
direct sense-warrant for the existence of the down-pull while 
putting the weights on the pan with our hands aud while 
