Vision in health and disease : the value of glasses for its restoration, and the mischief caused by their abuse : being the substance of lectures delivered at the Central London Ophthalmic Hospital / by Alfred Smee.
- Smee, Alfred, 1818-1877.
- Date:
- 1847
Licence: Public Domain Mark
Credit: Vision in health and disease : the value of glasses for its restoration, and the mischief caused by their abuse : being the substance of lectures delivered at the Central London Ophthalmic Hospital / by Alfred Smee. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![bodies when placed very obliquely. It consists of a concave glass dish, fluted on the outer side. This, when placed every ray of light impinging upon the in- ternal surface of the flutings obliquely, and transmits all, falling perpendicularly to the surface. As a result therefrom, the fluted glass becomes the best or most powerful reflector that can be constructed, and no appreciable light is lost by absorption. As the reflection takes place from the internal surface of the glass, there is no possibility of its being coated with dirt or other substance calculated to interfere with the result; more- over, by using pure white glass, white light is thrown upon the table; and if the flame be viewed through the shade its intensity is lessened, and it is rendered less injurious to the sight. The reflected rays are taken from that place where they arc naturally in excess; and hence, the table is not only more brilliantly illu- minated, but the light throughout the whole room is equalized. The onlv care required in the employment of the shade is the necessity of placing the light in its focus. (177.) There is a certain position in which objects should Ik? placed, in relation to the centre of light from which it is illuminated, which is in the highest degree important for the preservation of the organs of vision. I need hardly tell you that light is reflected from objects in such a way that the angle of reflection is equal to the angle of incidence. It is upon this prin- ciple that we obtain an image of an object from a looking-glass; and, although we cannot obtain a perfect image from the surface of pa]x'r, yet more light is reflected in that position. Wherever that reflection occurs it is destructive to vision, whether you sit by the sea-shore, and obtain the reflection from the sea, or are fishing on the banks of a river, and have the rays of the sun reflected to the eye, or are writing or reading from white paper at the reflecting angle. Opaque bodies, as pajx'r, &c., are found to reflect a greater amount of light if the rays fall very obliquely; hence the light ought to be placed nearly directly above the object viewed. (178.) The centre of light in the flame should on no account In? enabled to fall directly upon the eye, especially obliquely upon the under surface of the eye, or other lateral parts of vision, as in that position it is calculated to do much mischief. I was much surprised lately to observe that at one of our best libraries the light fell directly upon the inferior part of the eye, and caused much distress; and at another large establishment the parties](https://iiif.wellcomecollection.org/image/b22372015_0062.jp2/full/800%2C/0/default.jpg)
