Thomas Piketty has written a big book — 577 pages of text; 76 pages of notes; 115 charts, tables, and graphs — that has excited the left worldwide. First published in French in 2013, an English edition was issued last year to wide acclaim and a top position on theNew York Times bestseller list. It has been a long time since a technical treatise on economics has had such a market. An economist can only applaud. And an economic historian can only wax ecstatic.