Eight decades of astronomical seeing measurements at Mount Wilson Observatory

The astronomical seeing has been recorded at the Mount Wilson Observatory f or more than 80 years. Over this period of time, seeing measurements have b een made in a consistent fashion using the largest telescopes at the site. This provides an excellent record of the historical observing conditions ov er the life of the observatory. While the literature clearly shows that the intrinsic seeing on Mount Wilson is the best in the continental United Sta tes and comparable to that on Mount Haleakala, Hawaii, the historical recor d shows that, with the exception of a brief upswing during the period of th e Second World War, the number of subarcsecond seeing nights measured at th e 60 and 100 inch domes has been on the decline. We compare this record aga inst known events detailed in observatory reports and show that several of the low points in the seeing measurements correspond to periods of large-sc ale construction and development activity in the vicinity of the domes. Des pite the presence of weather-related variance in the year-to-year seeing, w e find no evidence for changes over a time period approaching 100 years.