54 
THE YOUNG SCIENTIST. 
of such a thing, and intimate that it has 
its foundation only in the mendacity of 
the relator, but it is true nevertheless. 
By what process of engineering does 
the comparatively small and feeble insect 
succeed in overcoming and lifting up, by 
mechanical means, the mouse or snake ? 
The solution is easy enough if we only 
give the question a little thought. 
The spider is furnished with one of the 
most efficient mechanical powers known 
to engineers, viz. : a strong, elastic thread. 
That the thread is strong is well known. 
Indeed there are few substances which 
will support a greater strain than the silk 
of the silkworm or the spider, careful ex- 
periment showing that for equal sizes the 
strength of these fibres exceeds that of 
common iron! But notwithstanding its 
strength, the spider's thread alone would 
be useless as a mechanical power if it were 
not for its elasticity. The spider has no 
blocks or pulleys, and therefore it cannot 
cause the thread to divide up and run in 
different directions, but the elasticity of 
the thread more than makes up for this, 
and renders possible the lifting of an 
animal much heavier than a mouse or a 
snake. This may require a little explana- 
tion. 
Let us suppose a child who can lift a six 
pound weight one foot, and do this forty 
times a minute. Furnish him with 350 
rubber bands, each capable of pulling six 
pounds through one foot when stretched. 
Let these bands be attached to a wooden 
platform on which stand a pair of horses 
weighing 2,100 lbs,, or rather more than a 
ton. If now the child will go to work and 
stretch these rubber bands, singly, hook- 
ing each one up as it is stretched, in just 
ten minutes he will have raised the pair 
of horses one foot! In other words, the 
elasticity of the rubber bands enables the 
child to divide the weight of the horses 
into 350 pieces of six pounds each, and at 
the rate of a little less than one per second 
he lifts these separate pieces one foot ! 
Each spider's thread acts like the elastic 
rubber bands. Let us suppose that the 
mouse w^eighed half an ounce and that each 
thread is capable of supporting a grain 
and a half. The spider would have to 
connect the mouse with the point from 
which it was to be suspended with 150 
threads, and if the little quadruped was 
once swung off his feet he would be power- 
less. By pulling successively on each 
thread and shortening it a little, the mouse 
or snake might be raised to any height 
within the capacity of the building or 
structure in which the work was done. 
So that to those who have ridiculed the 
story we may justly say: "There are 
more things in heaven and earth than are 
dreamed of in your philosophy." 
What object the spider could have had 
in this work we are unable to see. It may 
have been a dread of the harm which the 
mouse or snake might work ; it may have 
been the hope that the decaying carcasses 
would attract flies which would furnish 
food for the engineer. With this, how- 
ever, we are not so much concerned. Our 
object has been to explain and render 
credible some extraordinay feats of in- 
sect engineering. 
Bird Houses. 
A NEATLY-MADE bird house is not 
only a source of pleasure and profit, 
from the fact that it attracts the great 
friends of the gardener and keeps them 
about the place, but it is also an ornament, 
if properly located and constructed in 
harmony with its surroundings. Last 
year we gave several figures of bird houses 
with directions for making them, and we 
now give another which has a different ar- 
rangement and appearance, though chiefly 
constructed out of waste materials. The 
house shown in the accompanying engra- 
ving consists of four nine inch flower pots, 
resting on a base board shaped as we have 
figured it in the engraving. Through the 
centre of the base board there is inserted 
a pole, which passes through far enough 
to allow for the height of the flower pots 
and the thatched roof. 
The flower pots are placed around the 
pole, which is nailed to the base board. 
A hole is cut into the side of each pot for 
an entrance for the birds. The pots can 
be ornamented to suit the fancy, either 
with plaster of Paris, burrs and lichens, 
or they may be painted of some sombre, 
color. The second story of the house is 
