* SCIENCE Is published weekly on Friday, except the last week In December, and with an extra Issue in February by the American Association for the Advancement of Science, 1333 H Street, NW, Washington, DC 20005. Second-class postage (publication No. 484460) paid at Washington, DC, and at an additional entry. Now combined with The Scientific Monthly® Copyright C 1987 by the American Association ...

* SCIENCE Is pubilshed weekly on Friday, except the last week In December, and with an extra issue in May by the American Association for the Advancement of Science, 1333 H Street, NW, Washington, DC 20005. Secondclass postage (publication No. 484460) paid at Washington, DC, and at an additional entry. Now combined with The Sclentific Monthly® Copyright C 1986 by the American Association for th...

Context. The onset of gravitational collapse in cluster-forming clouds is still poorly known. Aims. Our goal is to use the Class 0 protostar IRAS 4A, which is undergoing collapse in the active molecular cloud NGC 1333, to set constraints on this process. In particular we want to measure the mass infall rate and investigate whether the collapse could have been triggered by a strong external pert...

* SCIENCE Is published weely on Friday, except the last week In Dece ber, by the AmeIcan AsocatIon for the Advancent of Scien, 1333 H Stret, NW, Washington, DC 20005. Second-dass postage (publication No. 484480) paid at Washington, DC, and at an additional entry. Now combined with The ScletIfc Monthly Copyright C 1986 by the American Association for the Advancement of Science. Domestic Individu...