  We present interferometric measurements of the Sunyaev-Zel'dovich (SZ) effect
towards the galaxy cluster Abell 370. These measurements, which directly probe
the pressure of the cluster's gas, show the gas distribution to be strongly
aspherical, as do the x-ray and gravitational lensing observations. We
calculate the cluster's gas mass fraction in two ways. We first compare the gas
mass derived from the SZ measurements to the lensing-derived gravitational mass
near the critical lensing radius. We also calculate the gas mass fraction from
the SZ data by deprojecting the three-dimensional gas density distribution and
deriving the total mass under the assumption that the gas is in hydrostatic
equilibrium (HSE). We test the assumptions in the HSE method by comparing the
total cluster mass implied by the two methods and find that they agree within
the errors of the measurement. We discuss the possible systematic errors in the
gas mass fraction measurement and the constraints it places on the matter
density parameter, OmegaM.
