New limit on the rate-density of evaporating black holes.

Data taken with the CYGNUS detector between 1989 September and 1993 January have been used to search for 1 second bursts of ultra-high-energy gamma rays from point sources at arbitrary locations in the northern sky. We find no evidence for such bursts. We set a theory-dependent upper limit on the rate-density of evaporating black holes of 8.5[times]10[sup 5] pc[sup [minus]3]yr[sup [minus]1] at the 99% C. L. When the same emission spectrum is used to recalculate previous upper limits based on direct searches, this limit is the most restrictive by nearly 2 orders of magnitude.