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Show 58 THE ACT OF SIGHT. pictur~ formed . on the retina of the eye, that gives ~s noti_ons of distance and also of magnitude. The format!on of th_at picture, though, as there is little doubt It does, It takes place in the living eye, is, after all, mer~ly a mechanical matter; and any one can_ produce I~ at pleasure, by closing the shutters, bormg a ~ole_ m them, placing a glass which is conyex, or thiCk m the middle, in the opening, and hold4 wg a sheet of paper at the proper distance behind. Not only th~t, but, by means of mirrors properly p~aced, or pnsms of glass, which reflect from their hmde~ surface~, we can convey those images of visible t~mgs whithersoever we will. That beautiful ~o~t~Ivan?e of Ramsden's, which, from being in itself mv1s~ble, Is called "Ramsden's ghost," is a remarkable mstanc~ of that. In a fine astronomical instru~~ nt for takmg the elevations of the celestial bodies. It IS nece~sarf that the plummet should, by means of the sp1~er s thread, or whatever other delicate substa~ce IS used for marking it, pass in a downwar~ line, from the very centre of the axis on which the mst~uf!Ient tl!rns to the very centre of the earth. The axis Itself Is enclosed in the workmanship so that the obseryer cannot see it, or make any di;ect reference to It for adjusting his instrument· but ~amsden's ghost bripgs_ it faithfully to his vie~, let the path be_ ever so mtncate or circuitous. On the ax_Je there _Is a .dot no bigger than a pin's point: one pnsm recmves t~e light from that, reflects it to another, that to a thtrd, and so on, till the picture of it is ~h~own upon the limb of the instrument, just where 1t Is crossed by the spiller's thread of the plummet. and a~ th?se prisms are all perfectly parallel, th~ reflectwn Is made to fall on the limb more exar.tly U!!der the ve:y cent~e of the axis than any one could dtscover by Immediate observation. Thus we can. by means that are pe:fectly mechanical, do even more t~an eyes can do m the forming of a picture on the retma. Therefore, we are warranted in con. PLEASURE OF IMAGINATION. 59 eluding, that that is not the act of sight, but that there is something mental consequent upon it, far more nice and curious than any thing which material eyes can discriminate .. And we have proof of it, in those pictured scenes which, sleeping or waking, arise to the imagination, far different from any thing that the eyes ever beheld, and yet equally bright and perfect in the colouring. But those i~agined views are, in truth, all made up of that which has been seen or otherwise perceived by the senses ; and, ther~fore, though, after observatio_n has given u~ the materials, we can, by the operatiOn . of ~:mr mmds, work it into endless forms and combmatwns of delight, we must obtain the materials origina~ly f~om observation. Nor must we forget to bear m mmd, that the case is here the same as it is everywhere else ; we cannot '; gather grapes of thorns, or figs of thistles;" we cannot build palaces of marble, 1f we have observed only mud and rushes. If our ob- } servation has been narrow, our imaginings must be meager; and if our observation has been vulgar, thev must be mean. The formation of those imagined works is perhaps the very highest pleasure we can enjoy, and it is the foundation of all that we invent and the greater part of what we do. If, therefore, we do not, by observation, find the mind sufficient materials whereon it may work, and out of which it may ela~orate valuable or splendid combinations, we cha1n ourselves down and are humble beings in the estimation of our n~io-hbours, and wretched in our own feelings: we not ~nly cut ourselves off from a vast volume of 1 enjoyment ; but we blight and wither our very powers of enjoying. The ennui that comes upon us when we have been long idle and listless, and the revery and oblivion which are consequent upon excess of mere thought, without the exercise and use of the senses, are proofs of the pleasure that we do derive, and |