Tariff
A tariff is called an optimal tariff if it's set to maximize the welfare of the country imposing the tariff. It is a tariff derived by the intersection between the "trade indifference curve" of that country and the offer curve of another country. In this case, the welfare of the other country grows worse simultaneously, thus the policy is a kind of "beggar thy neighbor policy". If the offer curve of the other country is a line through the origin point, the original country is in the "condition of a small country", so any tariff worsens the welfare of the original country.
Tariff
At the beginning of the 19th century, Britain's average tariff on manufactured goods was roughly 51 percent, the highest of any major nation in Europe. And even after Britain embraced free trade in most goods, it continued to tightly regulate trade in strategic capital goods, such as the machinery for the mass production of textiles. Thus seen, according to Bairoch, Britain's technological lead had been achieved ""behind high and long-lasting tariff barriers"".