Fifth book of lessons for the use of schools . by those bodies to our eyes. Let us now examine by what means the rays of lightproduce vision. They enter at the pupil of the eye, andproceeding to the retina, an expansion of the optic nerve,which is situated at the back of the eye-ball, they describethe figure, colour, and (with the exception of size) form acomplete representation of the object from which they pro-ceed. If the shutters be closed, and a ray of lightadmitted through a small aperture, a picture may beseen on the opposite wall similar to that which is deli-neated on the retina of th
Fifth book of lessons for the use of schools . by those bodies to our eyes. Let us now examine by what means the rays of lightproduce vision. They enter at the pupil of the eye, andproceeding to the retina, an expansion of the optic nerve,which is situated at the back of the eye-ball, they describethe figure, colour, and (with the exception of size) form acomplete representation of the object from which they pro-ceed. If the shutters be closed, and a ray of lightadmitted through a small aperture, a picture may beseen on the opposite wall similar to that which is deli-neated on the retina of the eye; it exhibits a picture inminiature of the garden, and the landscape would beperfect were it not reversed. This picture is producedby the rays of light reflected from the various objectsin the garden, and which are admitted through the hole 332 FIFTH BOOK. in the window shutter. It is called a camera obscura,(dark chamber,) from the necessity of darkening theroom in order to exhibit it. The rays from the glittering weathercock at the tof. of the building A, represent it at a; for the weathercockbeing much higher than the aperture in the shutter, onlya few of the rays, which are reflected by it in anobliquely descending direction can find entrance rays of light moving always in straight lines, thosewhich enter the room in a descending direction willcontinue their course, in the same direction, and will,consequently, fall upon the lower part of the wall op-posite the aperture, and represent the weathercockreversed in that spot, instead of erect in the upper-most part of the landscape; and the rays of light fromthe steps, b, of the building, in entering the aperture,ascend, and describe them in the highest instead of thelowest part of the landscape) whilst the rays proceedingfrom the part which is to the left, describe it on thewall to the right. Those which are reflected by thewalnut-tree, c B, to the right, delineate its figure in thepicture to the left, c d. Thus
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Keywords: ., bookcentury1800, bookdecade1860, bookpublishermontrealjohnlovell
