Theophilus Van Kannel invented the revolving door in 1888. His design helped alleviate several problems associated with conventional doors. His revolving door served as an airlock, preventing the rapid influx of cold air to warm buildings. It also helped to keep out wind and street noise. The doors were especially useful when installed at the entrances of skyscrapers. In 1889, Philadephia awarded him the John Scott Medal for the usefulness of his invention to society. Around the same time, Van Kannel established the Van Kannel Revolving Door Company to make and market his doors and made several improvements to his original design. In 1907, International Steel bought the company, which survives today as the International Revolving Door Company. Revolving doors are now an integral part of most modern skyscrapers as well as many other buildings.