BLAST FURNACES by Bernd and Hilla Becher (The MIT Press: $60; 272 pp.). You loved their "Water Towers" of a few years back. Now this pair of photographing professors from the Dusseldorf Art Academy return with more than 200 pictures of, yes, blast furnaces. The central element of a steel plant, the humble blast furnace is an odd though sturdy beast, often burning continuously for 10 years before having to be shut down and overhauled. These photos, taken only on cloudy days over a period of nearly three decades, do more than dispassionately demonstrate the varieties of furnace styles in sites as various as Britain, Belgium, France, Austria, Germany and the United States. They present the big fellows as objects of undeniable fascination, with a look at once prehistoric and extraterrestrial, enormous structures that have the ability to appear simultaneously melancholy, threatening, even unexpectedly playful. Bet you can't look at just one.