"Diagram Illustrating the Principle of Streamlining", from Norman Bel Geddes' Horizons: A Glimpse into the Not Far-Distant Future (1932)
Like "Form", "Surface" can be an overused and under-theorized term. Contemporary architectural discourse sometimes deploys these two terms as straw men, indicators of what is right or wrong with Architecture. Whereas some critics decry pure architectural formalism as a vapid endeavor, others see a return to formalism as a way to reclaim intellectual ground for the discipline. The same could be said about issues of surface, often grouped under the idea of "affect." Yet authors like David Leatherbarrow and Mohsen Mostafavi have theorized the surface as a site of contestation between structure and skin, eventually reclaiming elements of the architectural surface - facade, cladding, etc - as proper subjects of architectural inquiry.
The trend continues. Log 13/14, a special double issue that looks at the architectural and historical legacies of May 1968, ends with a curious article by Alejandro Zaera Polo, principal of Foreign Office Architects. I say "curious", only because the article is almost devoid of any direct reference to 1968. Zaera Polo's charge is therefore to locate architecture's locus of political action in the envelope. The envelope, however, is conceptually different from the surface. Zaera Polo writes:
The envelope exceeds the surface by incorporating a much broader set of attachments. It includes the crust of space affected by the scale and physical dimension of the space contained ... It also involves the space that surrounds the object ... The envelope has the capacity to represent the ancient political role that articulates the relationships between humans and nonhumans in a common world. The envelope is the surface and its attachments And although Zaera Polo claims that there is no "unitary theory" of the envelope, the above definition seems to ring a familiar bell.
In 1934, American designer Norman Bel Geddes tackled the subject of aerodynamics in "Streamlining", an article for the November issue of The Atlantic Monthly. Bel Geddes' task was to educate laypeople on the scientific underpinnings of aerodynamic theory. Ely Jacques Kahn, one of the 20th century's most prominent skyscraper architects said it best in a letter to Bel Geddes after the publication of "Streamlining". Kahn writes:
As so you aptly put it, stream lining has, unfortunately, become as much of a fetish as functionailism, and we have streamlined ash cans and breakfast food. Perhaps if we know more of the scientific angle, we may be less inclined to so stupid things with design. The "scientific angle" Kahn is referring to is the boundary layer theorem by German aerodynamics theorist Ludwig Prandtl. In a 1904 paper entitled "Über Flüssigkeitsbewegung bei sehr kleiner Reibung" ("On the Motion of Fluids with Very Little Friction"), Prandtl theorized that the effects of friction occur near, not on the surface of a body traveling through the air. This friction causes the air immediately adjacent to the surface to "stick" to the surface, thus creating a "boundary layer" between the surface and the moving air. Bel Geddes provided a much more reductive reading of Prandtl's theories, writing:
At the beginning of the twentieth century Ludwig Prandtl assumed that all air forces resisting the motion of a body could be considered as acting within the boundary layer. The boundary layer is a layer of air which, because of the air's viscosity, tends to cling to the surface of a body. Its thickness varies with the size of the body - from one tenth of an inch in a two foot body to about twelve inches in a body several hundred feet long [...] In general it might be said that the boundary layer is kept in contact with the entire surface, the body is streamlined ... a condition easier to state than to fulfill [...] Because theory is incomplete, all practical advance in streamlining has had to be empirical and the aeronautical engineer has led the parade. Alhough Bel Geddes' research failed to mention subsequent advances in boundary layer theory, his statement nevertheless remains an important statement on the application of a complex scientific principle aimed at laypersons and design professionals.
Bel Geddes' "Streamlining" piece is interesting as it shows a designer that is spearheading an effort to give a design trend its proper intellectual context. Similar efforts in the future would not fare as well in the scientific community. A notable example would be Sigfried Giedion's use of "space-time", which Albert Einstein would mock in a letter to Erich Mendelsohn. Anticipating this kind of interaction between design and scientific culture, Bel Geddes kept open communications with the scientific establishment while researching his article for The Atlantic Monthly. He also sent reprints to scientists around the world and received general accolades for the treatment of this subject.
But what is more interesting is how the boundary layer theory anticipates Zaera Polo's statements from Log 13/14. Although Prandtl theorized the boundary layer, Bel Geddes located it within design culture -- and this is an important impulse, for there are important physical and conceptual similarities between Bel Geddes' evocation of the boundary layer and Zaera Polo's musings on the "envelope."
For starters, an envelope can be thought of a version of the boundary layer, one that substitutes the architectural object for the aerodynamic object. Zaera Polo, for example, alludes to an adjacent space that forms an important part of the envelope, an impulse that implies a type or architectural boundary layer. And if the boundary layer is the true locus of friction, then similarly, the envelope becomes the true locus of the "friction" of architectural discourse.
And if we take this correlation between aerodynamic theory and contemporary architecture discourse as true, then we are poised to provide a "yes, but" to Reyner Banham's charge from "The Machine Aesthetic" (1955) labeling early infatuations with aerodynamic forms by Le Corbusier, Gropius, and Mendelsohn as an "anti-Purist but eye-catching vocabulary of design"  -- in other words, a vapid formalism. The lesson to be gleaned from Bel Geddes' article also anticipates another important implication of Zaera Polo's theory of the envelope -- the advocacy of formalism can be a political act, but it must be an informed political act.
 Alejandro Zaera Polo, "The Politics of the Envelope" Log 13/14 (Fall 2008), 195.
 Ely Jacques Kahn to Norman Bel Geddes, November 28, 1934, Norman Bel Geddes Theater and Industrial Design Papers 1873-1964, Job 937 (926), T Box 174, WA-14a, Harry Ransom Center for the Humanities, University of Texas at Austin.
 See John D. Anderson, Jr., "Ludwig Prandtl's Boundary Layer", Physics Today (Dec., 2005), 42-48.
 Norman Bel Geddes, "Streamlining", The Atlantic Monthly (Nov., 1934), 154-5.
 Reyner Banham, "The Machine Aesthetic", The Architectural Review, Vol. 447, No. 700 (Apr., 1955), 228.