Fine-scale anisotropy of the microwave background: an upper limit at lambda = 3.5 millimeters

Using the 36-foot NRAO telescope1 at A - 3.5 mm, we have set an upper limit of 0.0043 K, with 90 percent confidence, on the fluctuations in the cosmic microwave background. The angular scale of the measurement was 80". If discrete sources produce all of the microwave background, their number must exceed 0.35 Mpc-3. Subject headings: cosmic background radiation - cosmology - radio radiation