101 
Oct. i, 1885.] The Australasian Scientific Magazine. 
which have vexed the minds of all sorts and conditions of men from the 
simple thimble-rigger or three-card man to the nearly infallible bookmaker 
to those of the actuary who discerns the probability of issue to a first, 
second, or third marriage, and the chance of any one of problematical 
children becoming heir to the peerage of the Duke of Southdown-Merino, 
and to his colossal estates in Australia, and who can tell the honourable 
Mr. Youngerson the exact value of his interest in the great duke’s pile. 
( To be continued ). 
THE LENGTH OF THE DAY, 
BY 
WILLIAM WHEWELL, M.A. 
Let us consider the time of the revolution of the earth on its axis ; and 
we will find here also that the structure of organised bodies is suited to this 
element ; that the cosmical and physiological arrangements are adapted to 
each other. 
We can very easily conceive the earth to revolve on her axis faster or 
slower than she does, and thus the days to be longer or shorter than they 
are, without supposing any other change to take place. There is no 
apparent reason why this globe should turn on its axis just 366 times while 
it describes its orbit round the sun. 
The revolutions of the other planets, so far as we know them, do not 
appear to follow any rule by which they are connected with the distance 
from the sun. Mercury, Venus, and Mars have days nearly the length of 
ours. Jupiter and Saturn revolve in about ten hours each. For anything 
we can discover, the earth might have revolved in this or any other smaller 
period ; or we might have had, without mechanical inconvenience, much 
longer days than we have. 
But the terrestrial day, and consequently the length of the cycle of light 
and darkness, being what it is, we find various parts of the constitution 
both of animals and vegetables, which have a periodical character in their 
functions, corresponding to the diurnal succession of external conditions ; 
and we find that the length of the period, as it exists in their constitution, 
coincides with the length of the natural day. 
The alternation of processes which takes place in plants by day and 
by night is less obvious, and less obviously essential to their well-being, than 
