NAUTILUS was designed to observe the gravitational waves produced by collisions between objects such as black holes or neutron stars. According to the Frascati's group calculations, signals from such events could be masked by cosmic-ray showers. To take this effect into account they surround the cylinder with 116 cosmic ray detectors. When the aluminium cylinder vibrates from the effects of the gravitational waves, a transducer converts the mechanical signal into a electrical signal, which is in turn amplified and recorded. The group compared the signal from the cylinder with that from the cosmic-ray detectors over a three month period, and found that both the cosmic-ray detectors and the gravitational-wave detector registered events simultaneously on several occasions. The mechanical vibration of the cylinder - as small as 10-18 metres - corresponds to an energy deposit of 10-6 eV. According to the paper, future detectors operating near the quantum noise limit (i.e. cooled to 10-7 Kelvin) would have to be put underground to limit this cosmic interference.