feet
in width could not endure the winds and waves of a navigable lake, or
the wear and "swash" of a canal twelve feet deep on either side; and
the fact that Cortez navigated the ditches in the rainy season
establishes the insignificant size of his famous brigantines.

As the level of the surface of the land and the surface of the water at
Mexicalzingo, at Mexico, and at the village Tezcuco, does not
materially vary now from what it was in the time of Cortez, if we can
take for data the foundations of the church built by the Conquistadors
at these several places, we shall have to look to another quarter for a
supply of water for the city canals, which were sufficiently capacious
for canoe navigation. This supply we readily obtain by allowing the
waters of the canals Tacubaya and Chalco to pass through the streets of
the city in ditches sufficiently large for canoes, instead of passing
along the south and east fronts outside. By this hypothesis we obtain a
current, a prerequisite to the very idea of a canal, particularly in
the streets of a city.

The _savans_ of Europe have shown their profound ignorance of the first
principles of canal navigation in taking it for granted that the canals
of Mexico were filled with stagnant water, that had "set back" from the
stagnant pond of Tezcuco; and that the level of the pond must at all
times have been so high as to fill the canals, thus keeping the city in
constant danger from any sudden rise in the laguna. But, aside from the
rules of canal construction, there is an important sanitary question
involved. The present ditches in the middle of the streets, though they
have a perceptible current, and a slight infusion of _tequisquite_,
are an intolerable nuisance, and have a deleterious effect upon the
public health. How much more so must they have been when, from the
uncleanly habits of the Indians, they were the common receptacle of all
kinds of filth, and were constantly stirred up to their very bottoms by
the setting-poles of the navigators? The system of canalling is a
system of slack-water navigation, but abhors stagnant water.

We come next to the question of the dimensions of these street canals.
We know that they were intended only for the navigation of Indian
canoes; that two of them, which intersected the causeway of the night
retreat, Cortez crossed with his army, all of them climbing down into
the canal, wading across, and then climbing up on the other side while
load