  We have detected the Sunyaev-Zel'dovich (SZ) increment at 850 microns in two
galaxy clusters (Cl 0016+16 and MS 1054.4-0321) using SCUBA (Sub-millimetre
Common User Bolometer Array) on the James Clerk Maxwell Telescope. Fits to the
isothermal \beta model yield a central Compton y parameter of (2.2 \pm 0.7) x
10^{-4} and a central 850 micron flux of \Delta I_{0} = 2.2 \pm 0.7 mJy/beam in
Cl 0016. This can be combined with decrement measurements to infer y = (2.38
\pm_{0.34}^{0.36}) x 10^{-4} and v_{pec} = 400 \pm_{1400}^{1900} km/s. In MS
1054 we find a peak 850 micron flux of \Delta I_{0} = 2.0 \pm 1.0 mJy/beam and
y = (2.0 \pm 1.0) x 10^{-4}. To be successful such measurements require large
chop throws and non-standard data analysis techniques. In particular, the 450
micron data are used to remove atmospheric variations in the 850 micron data.
An explicit annular model is fit to the SCUBA difference data in order to
extract the radial profile, and separately fit to the model differences to
minimize the effect of correlations induced by our scanning strategy. We have
demonstrated that with sufficient care, SCUBA can be used to measure the SZ
increment in massive, compact galaxy clusters.
