Schaw. — On the Reflection of Light. 535 



Art. LXI. — On some Peculiar Cases of the Reflection of Light. 



By Major-General Schaw, C.B., B.E. 



[Read before the Wellington Philosophical Society, 17th October, 1894.] 



Plate XLVI. 



The reflection of light from smooth water or water agitated 

 by gentle ripples is a natural phenomenon which is familiar to 

 to us all, whether the light be that of the sun, or moon, or 

 a brilliant planet like Jupiter, or of artificial lights like those in 

 a harbour or on board ships ; but in all these cases we see the 

 light as well as its reflection doubling it in the water. There 

 are cases, however, in which we observe only the reflection, 

 the source of the light which is reflected being hidden from us ; 

 and such cases are at first somewhat puzzling. One such 

 case I observed about this time last year, and I have seen it 

 again this year during calm bright weather a little before sun- 

 set. It is only in spring and autumn that the phenomenon is 

 observable from my point of view, although doubtless it would 

 be seen at other times of the year, when the sun sets farther 

 north or south, from other points of view. 



The window of my sitting-room in Aurora Terrace is 

 about 180ft. above the sea, and it faces towards Clyde Quay, 

 or south-east. When the sun is lowering towards the west, 

 and is not visible from my window, a singular appearance of 

 reflected light is often to be seen on the comparatively calm 

 surface of the water towards the Te Aro Baths ; and at first I 

 was unable to trace the source or sources whence the reflection 

 came. None of the windows of the houses on the hill-side 

 above the water showed any bright reflection of the sun; 

 nevertheless the reflection was due to some of these windows, 

 as appeared evident on consideration, and as will be seen from 

 the annexed diagrams (Plate XLVI.). 



First, let us look at the course of the sun's rays as seen in 

 section, or looked at sideways. At the time when the bright 

 reflected patch of light was visible on the water at W from 

 the point of observation at O, the sun was at such a height 

 that the ray of light in the direction S H was reflected down- 

 wards to the water at W, and thence again upwards to the 

 eye at ; the angles of incidence and reflection in both cases 

 being of course equal. The reflection at W was repeated 

 many times on various inclined surfaces of minute wavelets, 

 and so produced a patch of sparkling light of some size, con- 

 siderably larger than the window whence the light was re- 

 flected. The reflection of the sun from the window was not 



