Fueled by a scarcity of land and by demand from multimillionaires willing to pay record prices for helicopter views of Central Park and beyond, Manhattan developers are building ever taller, ever thinner apartment buildings on ever tinier lots. Clustered mostly in and around West 57th Street, these skinny skyscrapers are reaching heights of more than 1,000 feet.

One consequence of beanstalk proportions: The higher and slimmer buildings get, the more they tend to sway at the top.

On a typically breezy day, a tower 1,000 feet tall might move a couple of inches, according to Rowan Williams Davies and Irwin, consulting engineers. About once a year, a 50-mile-per-hour wind comes up, moving a tower of this size about half a foot. On a rare day, say once every 50 years, 100-mile-per-hour winds might move the tower as much as two feet.

While such movement does not present a safety hazard and is often imperceptible, it can make some people woozy. So developers of skinny skyscrapers are installing giant counterweights, or dampening systems, at the apex of their towers to offset building motion. This ballast is not an amenity proclaimed in large type in a glossy brochure — or one most developers care to talk about. Nevertheless, it is viewed as state-of-the-art assurance for the penthouse-buying set.