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Cosmic rays have been something of a puzzle since they were discovered at the start of the 20th Century. In Cosmic Bullets Roger Clay and Bruce Dawson describe the work that has been done to try to solve this puzzle. The book has plenty of interesting information about cosmic rays, but I felt that it didn't have the buzz that it could have done. I thought the authors could have done more to some of the excitement of working in the field, and to indicate how explaining cosmic rays was an important part of cosmology in the 1930-1960 period. So you should read this book if you want to find out about cosmic rays, but I wouldn't particularly recommend it as recreational reading.
The book starts with the discovery of cosmic rays and shows how their investigation went hand in hand with the invention of new types of particle detectors. Throughout the book the problem of explaining the spectrum of energies is discussed, showing why high energy cosmic rays can't travel more than 300 million light years, and how lower energy particles will be greatly influenced by the galactic magnetic field. The later part of the book looks at the cosmic ray detectors which have been developed recently, leading up to the giant Auger project. However, the book was written nearly 10 years ago, and so doesn't have a great deal of information on this project.