792 Marvels of the Universe 
the ground ; the denser strata are above and the rays bent upwards. In the Polar phenomena the 
denser air is below, the rays are bent downwards and objects below the horizon are thrown up 
(Everett). An appearance similar to Mirage may be obtained by gently pouring alcohol or methy- 
lated spirit upon water (without mixing) in a vessel with glass sides. The spirit, though specifically 
lighter, is optically denser than the water and rays traversing the layer of transition are bent up- 
wards, so that the surface appears like a mirror when looked at very obliquely by an eye above it. 
SPIDERS] WEBS 
WE recently dealt in these pages with the wonderful spinning apparatus of the Spider, so that there 
is no need on the present occasion to explain how the substance of which the web is composed is 
elaborated. We desire rather to call the attention 
to a few of the many diverse types of architec- 
ture adopted by the different groups or genera of 
Spiders. There are two of these types that are 
known to all of us, though to some of us, it may 
be, only in a vague sort of way, because these 
objects are too commonplace to have attracted 
our serious attention. Some spiders employ their 
silk-producing faculty for the purpose of making 
underground tubes and tunnels which they conceal 
by artfully contrived trap-doors in which the silken 
threads are also used for holding the earthen 
door together and for forming its hinges. Others, 
which are hunters rather than trappers, construct 
no snares and reserve their silk for the elaboration 
of their egg-cocoon only. 
One can get some idea of the evolution of the 
web-weaving skill of the Spider by watching the 
weeds along a hedgerow, the branches of the hedge 
itself, young trees on the edge of the wood, the 
furze-bushes on the heath, which will show us webs 
of different degrees of complexity ranging from 
aes Pe ee the simple single line to the large wheel-like 
Do OR ENTE GER | SUICERNINS GH Une Cando Qoidler, wnltin itis wadiathing 
its short connecting lines which turn 
« = , 
This photograph shows the beaded character of the spokes, 
spiral threads, which converts the web into a trap to which it into a net, and the deadly effectiveness of the 
flies adhere, apart from any entangling of their limbs. 
“< , 
additional cross-lines with their minute spherules 
of gum that make it very difficult for any trapped insect to make its escape. This elaborate struc- 
ture, which we unthinkingly destroy with a slash of our walking-stick, has been constructed with 
considerable labour, and on a definite plan. Similar works schemed and carried out by man are 
said to be the result of much serious thought, the application of scientific principles, and so forth ; 
but when done by the lower animals, the philosophers tell us it is purely the result of certain reflex 
actions of an automatic nature, and with that lucid explanation we have to be content. 
If we stand before a web of the Garden Spider, such as that shown in the photograph on page 
795, we shall note that the whole structure is suspended from a more or less horizontal line that 
extends from one bush or branch to another ; and the throwing this line across the gap is the initial 
difficulty that this little engineer has to overcome. Relative to the size of the Spider the space to 
be bridged is enormous. But the Spider effects her purpose in a very simple way. Climbing out 
