  In many cosmological models, the large angular scale anisotropy in the cosmic
microwave background is parameterized by a spectral index, $n$, and a
quadrupolar amplitude, $Q$. For a Peebles-Harrison-Zel'dovich spectrum, $n=1$.
Using data from the Far Infra-Red Survey (FIRS) and a new statistical measure,
a contour plot of the likelihood for cosmological models for which $-1 < n < 3$
and $0 \le Q \le 50~\mu{\rm K}$ is obtained. We find that the likelihood is
maximum at $(n, Q) = (1.0, 19 uK)$. For constant $n$ the likelihood falls to
half its maximum at $Q \approx 14 uK$ and $25 uK$ and for constant $Q$ the
likelihood falls to half its maximum at $n \approx 0.5$ and $1.4$. Regardless
of $Q$, the likelihood is always less than half its maximum for $n < -0.4$ and
for $n > 2.2$, as it is for $Q < 8 uK$ and $Q > 44$.
