Short Papers and Notes. 33 
admirable adaptability to the exposed situation chosen by this 
bird for incubation. Birds that build their nests in holes, such as 
the owl, for instance, lay round eggs, which run no risk of being 
rolled about and smashed. Were the owl and Guillemot to 
change positions for a while, the latter would stand a fair chance 
of speedy extermination, affording a beautiful illustration of the 
profound wisdom which has been brought to bear in the working 
out of the grand problem of preservation. As a further illustration, 
let us take the eggs of the golden or green plover, and consider for 
a minute their shape, number, and colour. In the first place, like 
that of the Guillemot, they are laid on an almost flat surface in bleak 
moorland districts, often on the summit of a little knoll, to pre- 
serve them from being swamped by heavy rains. In the second 
place, they are very large eggs for the size of the bird. How 
wisely this difficulty is met and surmounted ; for all their sharp 
points meet in the centre, and practically form a square, so that 
the bird may be enabled to cover them all at the same time ; 
whereas, if she laid five eggs it would be almost impossible for her 
to hatch them all successfully. He who is curious enough to turn 
the round end of a plover’s egg into the centre of the nest, and 
walk away a respectful distance, will find on his return the parent 
bird has discovered the chaos in her little household, and speedily 
set matters right again. In the third place, the beautiful harmony 
of colouring of the eggs with their surroundings renders them 
difficult to find; and still further, the eggs are laid at a season 
when they are least likely to be addled by snow-storms.—/vom 
“ Familiar Wild Birds.” 
Erperimental Optics, 
Lord Rayleigh, the newly-appointed Professor of Natural Phi- 
losophy at the Royal Institution, in the place of Professor Tyndall, 
recently delivered the first of a course of lectures under the above 
title, illustrated by the electric light, observing that the new light 
afforded convenient opportunities of experiment that were 
unknown to Newton, Thomas Young, and Fresnel. Commencing 
with the question of the enfeeblement of light by distance, he 
mentioned that it appeared a strange coincidence that two 
theories so widely apart from the corpuscular or emission theory 
of Newton (the theory that light consists in particles travelling 
outward from a source) and the wave or undulatory theory of 
Thomas Young should both equally be able to account for this 
phenomenon. Yet on consideration it was seen that in both there 
was assumed a something travelling outwards from the source, and 
hence the explanation of enfeeblement by spread in travelling. 
Practical methods of photometry such as are in common use, with 
