Today in US history on March 29: Mad Bomber panic, Rosenberg trial, Keeling Curve’s CO₂ measurement

Today in US history, March 29 has marked a series of notable moments in US history, spanning public safety scares, landmark legal developments, scientific discoveries, and unusual natural events. From bomb threats that rattled New York City to pioneering climate measurements that reshaped environmental science, the day reflects a mix of social, political, and scientific turning points.

1951: ‘Mad Bomber’ scare unsettles New York City

On March 29, 1951, a homemade device exploded at Grand Central Terminal, startling commuters but causing no injuries. In the months that followed, five more bombs were discovered at major landmarks across New York City, including the public library. Authorities concluded the incidents were linked to the so-called “Mad Bomber."


History.com recounts it as the first known incident connected to the figure, dated back to November 16, 1940, when a pipe bomb was left in the Edison building with a note targeting Con Edison. Additional bombs surfaced in 1941, until a December message claimed the attacks would pause during World War II, with threats to resume later.

1951: Rosenbergs convicted of espionage

On this day in one of the most sensational trials in American history, Julius Rosenberg and Ethel Rosenberg were convicted of espionage for passing atomic secrets to the Soviets during and after World War II. The couple were later sentenced to death and executed in 1953.

1799: New York’s gradual abolition law

In 1799, New York passed a gradual abolition law declaring children born to enslaved mothers free, though they were required to serve their mother’s enslaver until age 25 for women and 28 for men.

1958: Start of the Keeling Curve measurements

On March 29, 1958, scientist Charles David Keeling recorded the first comprehensive measurements of atmospheric CO₂ at the Mauna Loa Observatory, finding a concentration of 313 ppm. His work led to the creation of the Keeling Curve, which revealed the steady rise of CO₂ in Earth’s atmosphere. The monitoring, initially funded during the International Geophysical Year, continues today.

Other notable events on March 29

• 1806: Construction authorized for the Cumberland Road, later known as the Great National Pike.
• 1852: Ohio limits working hours, making it illegal for children under 18 and women to work more than 10 hours a day.

1848: Niagara Falls briefly falls silent

On March 29, 1848, an enormous ice jam formed at the source of the Niagara River near Lake Erie. The blockage halted the flow of water over Niagara Falls, creating an eerie silence that lasted until the ice broke and the river resumed its course.