  We present the first measurements of the weak gravitational lensing signal
induced by the large scale mass distribution from data obtained as part of the
ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in
this analysis are from the Wide Synoptic Survey, which aims to image ~170
square degree in five filters. We have analysed ~22 deg2 (31 pointings) of i'
data spread over two of the three survey fields. These data are of excellent
quality and the results bode well for the remainder of the survey: we do not
detect a significant `B'-mode, suggesting that residual systematics are
negligible at the current level of accuracy. Assuming a Cold Dark Matter model
and marginalising over the Hubble parameter h=[0.6,0.8], the source redshift
distribution and systematics, we constrain sigma_8, the amplitude of the matter
power spectrum. At a fiducial matter density Omega_m=0.3 we find
sigma_8=0.85+-0.06. This estimate is in excellent agreement with previous
studies. Combination of our results with those from the Deep component of the
CFHTLS enables us to place a constraint on a constant equation of state for the
dark energy, based on cosmic shear data alone. We find that w_0<-0.8 at 68%
confidence.
