other. And this dissimilarity in the degree which it obtains, one might naturally deem a defect--the result of some slight inaccuracy in the drawing. Should not portraits of the same individual, if all perfect likenesses of him, be all perfectly like one another? No; not at all. A man at one moment of time, and seen from one particular point of view, may be very unlike himself when seen at another moment of time, and from another point of view. We have at present before us the photographic likenesses of four several individuals--three likenesses of each--and no two in any of the four sets are quite alike. They differ in expression, according to the mood which prevailed in the mind of the original at the moment in which they were imprinted upon the paper. In some respects the physiognomy seems different; and the features appear more or less massy in the degree in which the lights and shadows were more or less strong, or in which the particular angle they were taken in brought them out in higher or lower relief. We shall venture just one remark more on these very interesting drawings. The subject is so suggestive of thought at the present stage, that it would be no easy matter to exhaust it; and it will, we have no doubt, be still more suggestive of thought by and by; but we are encroaching on our limits, and must restrain ourselves, therefore, to the indication of just one of the trains of thought which it has served to originate. Many of our readers must be acquainted with Dr. Thomas Brown's theory of attention,--'a state of mind,' says the philosopher, 'which has been understood to imply the exercise of a peculiar intellectual power, but which, in the case of attention to objects of sense, appears to be nothing more than the co-existence of desire with the perception of the object to which we are said to attend.' He proceeds to instance how, in a landscape in which the incurious gaze may _see_ many objects without _looking_ at or knowing them, a mere desire to know brings out into distinctness every object in succession on which the desire fixes. 'Instantly, or almost instantly,' continues the metaphysician, 'without our consciousness of any new or peculiar state of mind intervening in the process, the landscape becomes to our vision altogether different. Certain parts only--those parts which we wished to know particularly--are seen by us; the remaining parts seem almost to have vanished. It is as if everything before had been but the doubtful colouring of enchantment, which had disappeared, and left us the few prominent realities on which we gaze; or rather as if some instant enchantment, obedient to our wishes, had dissolved every reality beside, and brought closer to our sight the few objects which we desired to see.' Now, in the transcript of the larger _tableau vivant_ before us--that which represents Dr. Chalmers seated among his friends on the Moderator's chair--we find an exemplification sufficiently striking of the laws on