at the time. Seizing upon a new development to visualize particle tracks, created by Donald Glaser and known as a bubble chamber, Alvarez realized the device was just what was needed, if only it could be made to function with liquid hydrogen. Hydrogen nuclei, which are protons, made the simplest and most desirable target for interactions with the particles produced by the Bevatron. He began a development program to build a series of small chambers, and championed the device to Ernest Lawrence. The Glaser device was a small glass cylinder () filled with ether. By suddenly reducing the pressure in the device, the liquid could be placed into a temporary superheated state, which would boil along the disturbed track of a particle passing through. Glaser was able to maintain the superheated state for a few seconds before spontaneous boiling took place. The Alvarez team built chambers of 1.5 in, 2.5 in, 4 in, 10 in, and 15 in using liquid hydrogen, and constructed of metal with glass windows, so that the tracks could be photographed. The chamber could be cycled in synchronization with the accelerator beam, a picture could be taken, and the chamber recompressed in time for the next beam cycle. This program built a liquid hydrogen bubble chamber almost long, employed dozens of physicists and graduate students together with hundreds of engineers and technicians, took millions of photographs of particle interactions, developed computer systems to measure and analyze the interactions, and discovered families of new particles and resonance states. This work resulted in the Nobel Prize in Physics for Alvarez in 1968, "For his decisive contributions to elementary particle physics, in particular the discovery of a large number of resonant states, made possible through his development of the technique of using hydrogen bubble chambers and data analysis." Scientific detective In 1964 Alvarez proposed what became known as the High Altitude Particle Physics Experiment (HAPPE), originally conceived as a large superconducting magnet carried to high altitude by a balloon in order to study extremely high-energy particle interactions. In time the focus of the experiment changed toward the study of cosmology and the role of both particles and radiation in the early universe. This work was a large effort, carrying detectors aloft with high-altitude balloon flights and high-flying U-2 aircraft, and an early precursor of the COBE satellite-born experiments on the cosmic background radiation (which resulted in the award of