THE MERCHANT BANKERS by Joseph Wechsberg. 365 pages. Little, Brown. $6.95.
London's dynastic Hambro family, the world's biggest merchant bankers, started their moneymaking art two centuries ago, when a Hambro sea captain got word that the Queen of Denmark had died in Paris; he promptly cornered the market for crape in Copenhagen. Britain's Baring banking clan made a great leap forward by arranging an $11,250,000 bond issue for Thomas Jefferson's Louisiana Purchase. The Rothschilds of Paris and London grew to prominence by smuggling millions in gold through Napoleon's line to Wellington's forces in...