by this happier experience, I recommenced to inquire among
scientific men, and soon found scattered instances of what I sought,
though in by no means the same abundance as elsewhere. I then
circulated my questions more generally among my friends and through
their hands, and obtained the replies that are the main subject of
this and of the three next chapters. They were from persons of both
sexes, and of various ages, and in the end from occasional
correspondents in nearly every civilised country.

I have also received batches of answers from various educational
establishments both in England and America, which were made after
the masters had fully explained the meaning of the questions, and
interested the boys in them. These have the merit of returns derived
from a general census, which my other data lack, because I cannot
for a moment suppose that the writers of the latter are a haphazard
proportion of those to whom they were sent. Indeed I know of some who,
disavowing all possession of the power, and of many others who,
possessing it in too faint a degree to enable them to express what
their experiences really were, in a manner satisfactory to themselves,
sent no returns at all. Considerable statistical similarity was,
however, observed between the sets of returns furnished by the
schoolboys and those sent by my separate correspondents, and I may
add that they accord in this respect with the oral information I
have elsewhere obtained. The conformity of replies from so many
different sources which was clear from the first, the fact of their
apparent trustworthiness being on the whole much increased by
cross-examination (though I could give one or two amusing instances
of break-down), and the evident effort made to give accurate answers,
have convinced me that it is a much easier matter than I had
anticipated to obtain trustworthy replies to psychological questions.