Mr. Flinders Petrie, a contributor of interesting experiments on kindred subjects to Nature, informs me that he habitually works out sums by aid of an imaginary sliding rule, which he sets in the desired way and reads off mentally.  He does not usually visualise the whole rule, but only that part of it with which he is at the moment concerned (see Plate II.  Fig. 34, where, however, the artist has not put in the divisions very correctly).  I think this is one of the most striking cases of accurate visualising power it is possible to imagine.

I have a few returns from chess-players who play games blindfolded; but the powers of such men to visualise the separate boards with different sets of men on the different boards, some ivory, some wood, and so forth, are well known, and I need not repeat them.  I will rather give the following extract from an article in the Pall Mall Gazette, 27th June 1882, on the recent chess tournament at Vienna:—­

“The modern feats of blindfold play (without sight of board) greatly surpass those of twenty years ago.  Paul Morphy, the American, was the first who made an especial study of this kind of display, playing some seven or eight games blindfold and simultaneously against various inferior opponents, and making lucrative exhibitions in this way.  His abilities in this line created a scare among other rivals who had not practised this test of memory.  Since his day many chess-players who are gifted with strong and clear memory and power of picturing to the mind the ideal board and men, have carried this branch of exhibition play far beyond Morphy’s pitch; and, contemporaneously with this development, it has become acknowledged that skill in blindfold play is not an absolute test of similarly relative powers over the board:  e.g. Blackburne and Zukertort can play as many as sixteen, or even twenty, blindfold games at a time, and win about 80 per cent of them at least.  Steinitz, who beats them both in match play, does not essay more than six blindfold at a time.  Mason does not, to our knowledge, make any specialite at all of this sort.”

I have many cases of persons mentally reading off scores when playing the pianoforte, or manuscript when they are making speeches.  One statesman has assured me that a certain hesitation in utterance which he has at times, is due to his being plagued by the image of his manuscript speech with its original erasures and corrections.  He cannot lay the ghost, and he puzzles in trying to decipher it.

Some few persons see mentally in print every word that is uttered; they attend to the visual equivalent and not to the sound of the words, and they read them off usually as from a long imaginary strip of paper, such as is unwound from telegraphic instruments.  The experiences differ in detail as to size and kind of type, colour of paper, and so forth, but are always the same in the same person.

A well-known frequenter of the Royal Institution tells me that he often craves for an absence of visual perceptions, they are so brilliant and persistent.  The Rev. George Henslow speaks of their extreme restlessness; they oscillate, rotate, and change.