WITH THE INCUBATION OF BIRDS. 
607 
straw, lined with hair. The woodpecker and the parrot take to 
hollow trees ; but I hardly know an arboreal bird beside that 
constructs any nest that is not wholly covered or doomed over. 
Very many insects that are exposed to the air during their 
metamorphoses weave coverings of silk and cotton, in which 
they lie shrouded, at once impenetrable to moisture and uninflu- 
enced by the disturbances of the atmosphere. It would seem 
that the object, whatever it be, is the same in both. It is not 
for warmth that the insects spin these webs, for they form their 
coverings of silk and cotton in the hottest period of the year ; 
and I find that, whilst all our birds that build open nests breed 
early, those that construct the doomed and spherical ones nestle 
in the season between the spring and autumnal rains, when the 
air is saturated with electricity, and is in a state of constant 
change. 
“ The destructive influence exercised by the active electricity 
of the atmosphere on the eggs of birds, accords with that organic 
gradation by which the high embryonic animals commence vege- 
tative life with an organization similar to that of the lower. The 
successive stages of development presented by the egg during in- 
cubation exhibit the heart and great vessels constructed like 
those of the Batrachian reptile, with reference to a bronchial cir- 
culation. In the descending scale of organization in animals, 
where the respiration is low and the irritability high, the electric 
stimulus is rapidly fatal. Fish and Crustacea perish in great 
numbers under the influence of a thunder-storm ; and the half- 
matured embryo in the egg is destroyed by the disturbances 
which prevail during the activity of the summer lightning. 
“ Electricity being entirely confined to the surface of bodies, 
and the quantities they are capable of receiving not following the 
proportion of their bulk, but depending principally upon the ex 
tent of surface over which it is spread, the exterior of bodies may 
be positively or negatively electric, while the interior is in a state 
of perfect neutrality. Under isolation the quiescent state of the 
electricity occasions no sensible change in their properties. The 
power of retaining the electric fluid depending upon the shape, 
and the sphere and the spheroid retaining it readily, while it 
escapes from a point, or is received by a point with facility, the 
enveloping the eggs of birds in dried and non-conducting ma- 
terials spread entirely and wddely round is a means of steadily 
maintaining an uniform distribution of the electricity, and with 
it of preserving that state of quiescence by which no sensible 
changes are communicated to the embryo within. Thus at a 
time when the air is excessively disturbed by explosions of light- 
ning and by shocks of thunder-storms, the business of incubation 
