536 Transactions. — Miscellaneous. 



directly visible at O, because the rays were thrown downwards 

 to W, not in the direction towards 0. The bright patch of 

 light persisted for some minutes, notwithstanding the revo- 

 lution of the earth, which causes the apparent downward 

 movement of the setting sun, both on account of a slight dis- 

 persion of the rays reflected from the window-panes, and also 

 and more specially on account of the varying inclinations of 

 the reflecting surfaces of the wavelets. 



But not only is it necessary that the eye should be at the 

 right level to see the reflection, the sun also being at the right 

 elevation to produce it, but also the position of the eye in 

 plan with reference to the direction of the sun's rays, and 

 the orientation of the wall of the house, a window in which 

 acts as the first reflecting mirror. This will be seen from the 

 plan showing the course of the sun's rays if seen from above. 

 The position of the setting sun in spring and autumn is 

 about as shown on the plan, and it will be evident that the 

 window acting as the first reflector must be such that the 

 angle it forms with the impinging ray is equal to that formed 

 by the reflected ray which reaches in consequence of its 

 second reflection from the surface of the water. If the build- 

 ing were in any other alignment the reflected ray would be 

 otherwise directed, and would not be seen at 0. 



It will be evident, also, why I only see this reflection at 

 this time of the year or in the autumn. When the sun sets 

 farther south in the summer, or when it sets farther north in 

 the winter, the reflections are thrown towards the north or 

 the south, and are not visible at O, as they are when the sun 

 is setting in the intermediate point. But by shifting the 

 point of observation the reflection no doubt would be seen 

 when the sun is at the same elevation, if the point of observa- 

 tion were at the same level, or, rather, in the same inclined 

 plane. 



The effect is the inevitable result of the law of reflection of 

 light from reflecting surfaces — viz., that the angles of inci- 

 dence and reflection are always equal and in opposite direc- 

 tions ; but, to see the effect, the eye, the vertical mirror (which 

 is the window), and the sun must be in the right positions to 

 fulfil the conditions of the law of reflection. 



A much more beautiful and astonishiug effect of reflection 

 is to be seen, however, under favourable circumstances under 

 the steep clay escarpment of the hill on which Mr. Fitz- 

 Gerald's house stands. This clay escarpment appears from 

 my window to be of a uniform reddish-yellow colour, with 

 patches of green bushes growing upon it. But when the sur- 

 face of the water at the base of the cliff is not agitated by 

 wind, and the afternoon sun is shining brightly on the cliff, 

 the reflection in the water is coloured in the most gorgeous 



