THE suggestion has several times been made that treatment of weather elements by days and months is arbitrary and unnatural for stations not within the Tropics.2 In latitudes subject to cyclones the distribution of weather elements depends largely upon the relation of cyclones and anticyclones ; and the cyclone is, therefore, a more rational unit than the day or the month. In the new 3rd edition of Hann's Handbuch der Klimatologie it is significant that a new section is added, dealing with recent suggestions as to the introduction of the cyclonic unit into climatological investigations.In order to find a method of treating weather by the cyclonic unit, it seemed wise to use data from a station where the cyclonic control is strong. There were available in the climatological laboratory of Harvard University data for parts of the years between 1887 and 1890 for Nashua, New Hampshire, a station in New England, 41 miles north-west of Boston and about 30 miles from the coast. The data do not represent the whole period, and the reason'for the omission of some weeks is not known to the writer. It is probable that the weeks omitted are those in which the cyclonic control is not marked, and the study is, perhaps, weakened by their absence. These data were used-because they were available, and because Nashua fulfils the conditions of a sbtion with strong cyclonic control. Ths data consist of thermograph and barogr,aph curves, and the wind direction and weather taken at noon, 6 p.m., midnight, and 6 a.m. Fig. 1 shows the curve for a typical winter week, and Fig. 2 that for a typical summer week.After the study for Nashua was completed, it seemed well to apply the results to data from another station ; and, consequently, the records for Boston for the months of January, February, and March 1909 were used as they were at hand, and the data had a present interest.While there have been several suggestions as to the advisability of treating weather by the cyclone, little has been said as to just what constitutes a cyclonic unit. The most obvious thing is, of course, a rise 1 A part of the work done in the course in climatological research given in Earvard Report 2 Ward, R. De C.-"Suggestions concerning a more Rational Treatment of Climatology." University under the direction of Prof. R. De C. Ward during the year 1908-1909.