The Shortt clock was replaced as the standard by quartz crystal clocks in the 1930s and 1940s. Quartz clock operation is based on a property of quartz crystals. If you apply an electric field to the crystal, it changes shape, and if you squeeze or bend it, it generates an electric field. When put in a suitable electronic circuit, the crystal can vibrate and generate an electric signal that can be used to operate an electronic clock display.
Quartz crystal clocks were better because they had no gears or escapements to disturb their regular frequency. Such quartz clocks continue to dominate the market in numbers because their performance is excellent and they are inexpensive.