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Excerpt from University of California Publications in Geography, Vol. 2: 1919-1929 Prior to the completion Of the twenty-five year period the ther mometers were exposed in a window shelter on the north side of the Students' Observatory Building. About a year before the transfer Of the meteorological station to the Department Of Geography a cooperative Observer's shelter of the United States Weather Bureau pattern was set up on the grounds south of the Observatory, and Observations were begun with a duplicate set Of thermometers in the new location, the window shelter Observations being continued. A study of comparative readings under the two conditions of exposure was undertaken in order to determine the amount of correction to be applied to the valuable series Of window shelter observations, that they might be made available for use in connection with the Observa tions taken in the new and better location. Day-by-day results Of this comparison are unfortunately not available in sufficient numbers to permit a detailed study of the amounts of the differences. It was necessary for the purposes of this thirty-year synopsis, however, to determine these differences as accurately as possible. Inspection of the data at hand indicates that different weather conditions have had different effects on the readings in the two locations, sometimes causing them to show only slight differences, at other times greater differences, and that at isolated and irregular times individual differences have been considerably in excess of the average. It is clear that such excessive departures may exert an undue influence on the means of the departures. Being irregular and Often widely separated in point of time they/do not tend to neutralize each other. A large difference, occurring only once in a month and hence by no means typical of average conditions, may cause the mean difference to appear excessive. In other words, the arithmetical mean of all the differences may not be the most