"Contradictory convention that sets up, on the one side, absolute authority, and, on the other, unlimited obedience." What does this mean?

It means that slavery is a tyrannical system.

Explanation:

This sentence was written by Jean-Jacques Rousseau and was aimed at explaining slavery as something tyrannical and suffocating, which does not allow the responsibility and the rights of each man over himself, because it makes some men have too much power over others, while other men have no alternative but to completely obey the powerful, losing their freedom, autonomy and responsibility over themselves and their own actions.

an effect of the steamboat's popularity was that people began building canals in the united states and europe. this was done to find another way to transport goods across the country and in that time, transportation using the river was very slow and dangerous. it depended entirely on manpower and the current of the river. that all changed in the late 1700's when steamboats were introduced. they soon revolutionized travel and trade through the river and dominated the waterways. eventually, other means of transportation took over from the steamboats, but there was a time that they the united states to expand to the west.