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a nuisance not to be able to lay hands on a bit of paper to mark the place in a book, every bit of paper on the table was sure to contain something not to be spared. I very quietly said that I always had a stock of bookmarkers ready cut, with a proper place for them: my readers owe many of my anecdotes to this absurd practice. My two colloquials burst into a fit of laughter; about what? Incredulity was out of the question; and there could be nothing foolish in my taking measures to avoid what they knew was an inconvenience. I was in this matter obviously their superior, and so they laughed at me. Much more candid was the Royal Duke of the last century, who was noted for slow ideas. 'The rain comes into my mouth,' said he, while riding. 'Had not your Royal Highness better shut your mouth?' said the equerry. The Prince did so, and ought, by rule, to have laughed heartily at his adviser; instead of this, he said quietly, 'It doesn't come in now.'

De Attentionis mensura causisque primariis. By J. F. Herbart. Kœnigsberg, 1822, 4to.

This celebrated philosopher maintained that mathematics ought to be applied to psychology, in a separate tract, published also in 1822: the one above seems, therefore, to be his challenge on the subject. It is on attention, and I think it will hardly support Herbart's thesis. As a specimen of his formula, let $t$ be the time elapsed since the consideration began, $\beta$ the whole perceptive intensity of the individual, $\phi$ the whole of his mental force, and $z$ the force given to a notion by attention during the time $t$. Then,

$z=\phi (1-\varepsilon ^{-\beta t})$

Now for a test. There is a jactura, $v$, the meaning of which I do not comprehend. If there be anything in it, my mathematical readers ought to interpret it from the formula

$v={\frac {\pi \phi \beta }{1-\beta }}\varepsilon ^{-\beta t}+C\varepsilon ^{-t}$:

and to this task I leave them, wishing them better luck than mine. The time may come when other manifestations of mind, besides belief, shall be submitted to calculation: at that time, should it arrive, a final decision may be passed upon Herbart.