another. The canals I have observed this year agree fairly within the errors of observation with those figured on Schiaparelli's chart.
The fact that in all cases they do not absolutely agree with his is the very best of proofs that they are substantially the same; for such slight discordance proves the absence of conscious psychic reproduction. It confirms by not conforming.
As, in observations of minute detail, the psychic element insensibly creeps in, it will be well to consider it for a moment. An idea is a force, a mode of motion, which, unless obstructed by other ideas, instantly and inevitably produces its effect upon whatever mind it may chance to impinge, just as light or electricity or any other mode of motion does, according to its kind. An easy instance of this can be got by asserting at dinner, before a company of connoisseurs, that the wine is slightly corked. Every one not actuated by a spirit of contradiction will at once perceive that it is so, and will continue to believe it, in many cases, after it is abundantly disproved. This is what takes place in the normal, unbiased—that is, so far as this idea goes—vacant mind. But minds have their familiar ideas, which an incoming idea is pretty sure to rouse, and these react to some extent upon the stranger, and color it with something of their own complexion. If we expect to meet
