34. (Pg. 175) What is that point denominated? 35. (Pg. 176) What is meant by a focus? 36. (Pg. 176) Why is the point behind the mirror, called the _imaginary focus_? 37. (Pg. 176) Why does an object appear to be lessened by a convex mirror, (fig. 2.)? 38. (Pg. 176) What is a concave mirror, and what its peculiar property? 39. (Pg. 176) How are parallel rays reflected by a concave mirror, as explained by fig. 3, plate 18? 40. (Pg. 177) Where is the focus of parallel rays, in a concave mirror? 41. (Pg. 177) If rays fall on it convergent, how are they reflected? 42. (Pg. 177) How if divergent? 43. (Pg. 177) How, and why, may concave, become burning mirrors? 44. (Pg. 178) Why may rays of light coming from the sun, be viewed as parallel to each other? 45. (Pg. 178) If a luminous body, as a burning taper, be placed in the focus of a concave mirror, how will the rays from it, be reflected? (fig. 6.) 46. (Pg. 178) What fact is explained by fig. 7, plate 18? CONVERSATION XVI. ON REFRACTION AND COLOURS. TRANSMISSION OF LIGHT BY TRANSPARENT BODIES. REFRACTION. REFRACTION BY THE ATMOSPHERE. REFRACTION BY A LENS. REFRACTION BY THE PRISM. OF COLOUR FROM THE RAYS OF LIGHT. OF THE COLOURS OF BODIES. MRS. B. The refraction of light will furnish the subject of to-day's lesson. _Caroline._ That is a property of which I have not the faintest idea. _Mrs. B._ It is the effect which transparent mediums produce on light in its passage through them. Opaque bodies, you know, reflect the rays, and transparent bodies transmit them; but it is found, that _if a ray, in passing from one medium, into another of different density, fall obliquely, it is turned out of its course. The ray of light is then said to be refracted._ _Caroline._ It must then be acted on by some new power, otherwise it would not deviate from its first direction. _Mrs. B._ The power which causes the deviation of the ray, appears to be the attraction of the denser medium. Let us suppose the two mediums to be air, and water; if a ray of light passes from air, into water, it is more strongly attracted by the latter, on account of its superior density. _Emily._ In what direction does the water attract the ray? _Mrs. B._ The ray is attracted perpendicularly towards the water, in the same manner in which bodies are acted upon by gravity.