Thirty-four "forked tracks" similar to two previously reported by Rochester and Butler have been observed in 11,000 cloud-chamber photographs of cosmic-ray penetrating showers, confirming their conclusion that new unstable neutral and charged particles exist. The lifetime of the neutral particles is found to be about 3X10 -10 sec, and some information as to the nature of the decay products is given.

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LETTERS TO THE EDITORin the proper energy channels were measured with and without GM counter umbrella in anticoincidence. The results showed an exponential time distribution with a mean life of 2.2±0.05 jusec. 1 The large area of the detector permitted collection of the cosmic-ray data in counting times of about 30 minutes for the complete determination.In the course of this work, several applications to problems of current interest were made. Cylindrical inserts, empty and open at the top, were placed in the large counter. A survey of native radioactive contamination of a number of shielding materials placed in the insert revealed that samples of stainless steel were very clean; mild steel was slightly active; while lead, tap water, and photomultiplier tubes were considerably contaminated. A live dog was lowered into the insert and counted before and after injection of a solution containing 10~7 curies of radium. It was concluded that a radium content of about 5X10 -9 curies could have been detected. By doubling up, a human being could be lowered into the counter which covered almost all of the solid angle. A number of people, men and women, were thus counted, with counting rates well above background. A water "human phantom" was made and a potassium salt dissolved in it. A counting efficiency of 10 percent for K 40 in this geometry was found. The counting rates from the human beings agreed well in most cases with the rate expected from the potassium in their bodies. Studies of neutron shielding external to the detector were also done.It is, of course, clear that phenomena which are distinguished by two or more events in delayed coincidence can be considered for study by means of such large detectors, and various inserts can be employed where needed, for instance, in the individual counting of the two gamma-rays from positron annihilation. Detailed discussions of investigations with the large detectors will be published in due course. The authors wish to thank L. Brown, R. Schuch, and Captain W. A. Walker for their assistance in the construction and testing of the detectors, C. W. Johnstone for the design of the electronic equipment, and T. J. White and D. Carter for help in computations.