BLUE HILL OBSERVATORY on January 30, 1905, completed its twentieth year?s work, and it is noteworthy that three out of its staff of four have been there at least eighteen years. Owing to the crowds of people brought to the hill by?the electric cars, it was found necessary in 1905 to enclose the observatory by wall and fence, some of the secondary instruments having previously been moved for the same reason. Blue Hill is one of the few American observatories where the standard instruments have remained in the same position and with unchanged environments for so long a time, so that, except for the fact that the times of observation were changed to agree with those made by the U.S. Weather Bureau, the records are all strictly comparable. Since 1901 the observations have all been published in the metric units, English units being. only used in parallel in the summaries.