From Hitchcock and Johnson, The International Style: Architecture Since 1922 (pp.66-67)

On American skyscrapers and verticality
¥ÒThe verticality of the skyscrapers of the American functionalists is obtained by reducing the window area and increasing the weight of the screen wall.  It also contradicts the storeyed character of the construction and destroys the human scale of the design.  In the early evening, when the lights come on, the solid towerlike quality of the skyscraper disappears.  Then, at least, it is seen as one volume divided up into horizontal storeys.  Only on rear elevations, or on facades where the architect has been severely restricted by economy, is the underlying horizontality of the American commercial building visible in the daytime.
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¥This artificial impression of solidity, this applied verticality, undoubtedly increases the visual congestion of the modern city.  The continual appeal of vertical lines tires the eyes.  Even the most commercial buildings of the nineteenth century provided the reposing horizontal of an approximately even cornice line.
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¥The verticality of the skyscraper is meaningless and anarchical.  Yet because the skyscraper is an American development and the international style has developed in Europe, some nationalist critics would protect our functionalist architects from the invasion of a horizontal aestheticÉ
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¥Horizontality is not in itself, however, a principle of the international styleÉ.The principle of regularity tends to increase the effect of general horizontality at the expense of the vertical elements which play but a subordinate part in most buildings.Ó