peaked forward within a 14° laboratory angle. The latest results also indicate that the total elastic-scattering cross section constitutes -1/3 of the total cross section in the energy range we have measured. This ratio has been indicated by a phenomenological black-sphere model of Koba and Takeda for a sphere radius of ~ln/m^c.'° It is surprising that the inelastic cross section does not decrease appreciably with increasing energy which may indicate a longer-range annihilation interaction than expected.^ The Ball-Chew theory/^ which is in agreement with the low-energy antiproton data, attributes the annihilation interaction to a rather short-range absorbing core. Of course the inelastic cross section as presented here includes both annihilation and meson production. From the partial analysis of the 948-Mev inelastic events, it appears that not more than about 10 mb of the inelastic cross section can be due to meson production. (The remaining 46 mb must then be attributed to annihilation.) This analysis is based on the assumption that production of 2 or more mesons is negligible except in annihilation. The assumption seems warranted because double meson production is known to be very small in nucleon-nucleon collisions at this energy.''''^^'^^ Upon completion of our analysis we hope to discuss more fully the inelastic process. In addition to the antiproton-proton cross sections, we have the antiproton-deuteron cross sections at the same five energies. These results will be presented in a later publication.

Twenty-two proton, neutron, and alpha jets (N h <3, 2X10 11 eV<£< 1.5Xl0 13 eV), found in a 22-liter emulsion stack flown for 13 h at an altitude of 116 000 feet, have been analyzed to identify the nature of the particles emitted in the extreme backward cm. cone. Among 82 tracks analyzed, out of 149 tracks traced (total length of the secondaries traced was 20.4 m and 74 interactions were found), 53 secondaries were attributed to pions, 18 to kaons, 10 to protons, and one to a hyperon. The relative composition of the 82 secondaries has a dependence on the cm. emission angle 0. For 0>175°, there were 7 x, 9 K, 10 p, and 1 Y; for 0<175°, there were 46 TT, 9 K, and no baryons. A similar distinction existed for the average cm. momenta

and the average transverse momenta in the extreme backward cm. emission angle;

becomes large and becomes small. The baryons carried the average fraction 0.5±0.2 of the total available energy in the cm. system. Concerning the K/ir ratio, p t distribution, and

at 0<175°, the hydrodynamical theory with a critical temperature kTc^m^c 2 predicts the correct behavior. In this region, the cm. momentum distribution of pions fits the form dNozp n dp with n= -0.8db0.4. But for the extreme backward cm. emission angle region, 0>175°, the smallness of and concentration of kaons and baryons favor an interpretation in terms of the Heisenberg theory. Rochester, edited by