. The principles of physics. ature of the cornea in different meridi-ans, so that when, for example, a diagram like Fig. 330 isheld at a distance, vertical lines willbe in focus and horizontal lines will beout of focus and will appear blurredand indistinct, or vice versa. Remedy:lenses of cylindrical curvature. But,for this, as well as for all other de-fects or troubles of the eyes, consulta skilled oculist, and the earlier thebetter. Advice to all: Do not overstrain orovertax the eyes, or use them in in-sufficient or excessive light, in flickering light such as that ofa gas-jet, or in unstead
. The principles of physics. ature of the cornea in different meridi-ans, so that when, for example, a diagram like Fig. 330 isheld at a distance, vertical lines willbe in focus and horizontal lines will beout of focus and will appear blurredand indistinct, or vice versa. Remedy:lenses of cylindrical curvature. But,for this, as well as for all other de-fects or troubles of the eyes, consulta skilled oculist, and the earlier thebetter. Advice to all: Do not overstrain orovertax the eyes, or use them in in-sufficient or excessive light, in flickering light such as that ofa gas-jet, or in unsteady light such as that in a movingvehicle ; and avoid so far as practicable sudden changes oflight, such as lightning flashes, etc. 392. Stereopticon. — This instrument is extensively em-ployed in the lecture-room for producing on a screen magnifiedimages of small, transparent pictures on glass, called slides;also for rendering a certain class of experiments visible to alarge audience by projecting them on a screen. The lime. Fl6. 330. >For useful information relating to the operation of projection, especially forscientific illustrations, see Wrights Light, and Dolbears Art of Projecting. STEREOPTICON. 433 light is most commonly used, though the electric light is -pre-ferred for a certain class of projections. The flame of anoxyhydrogen blow-pipe A (Fig. 331) is directed against astick of lime B, and raises it to a white heat. The radiations
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
