Alfred Marshall on Free Trade

Here is a gem of a quotation by Alfred Marshall on free trade, unearthed by Doug Irwin on p. 221 of his 1996 book Against the Tide: An Intellectual History of Free Trade: 

“[Free trade] is not a device, but the absence of any device. A device contrived to deal with any set of conditions must become obsolete when they change. The simplicity and naturalness of Free Trade–that is, the absence of any device–may continue to outweigh the series of different small gains which could be obtained by any manipulation of tariffs, however scientific and astute.”