OF THE ATMOSPHERIC TEMPEEATURE. 193 



The tabular numbers for five stations, having the longest series of observations, 

 are graphically represented on the accompanying plate. 



The greater irregularity for the shorter series is sufficiently well marked, and 

 the zigzag lines of the Salem temperature, derived from a 43 year series, are yet 

 inconveniently large for the purposes of comparison. 



The Marietta and Providence daily temperatures show many coincidences in the 

 zigzag lines or in the differences from their respective mean values and particularly 

 so in the vn7iter season ; the Portland temperatures, also, frequently conform to the 

 same fluctuations. From this we infer that changes from the normal temperatures 

 extend, especially in the winter season, over large tracts of country, and there are also 

 indications of the occurrence of the same phase about one day later in Rhode Island 

 than in Ohio, showing that the normal state of the weather has a tendency (especially 

 in the winter) to an easterly progression, the same as recognized in the case of 

 storms or unusual thermal disturbances of the atmosphere. About the 20th of 

 February, all stations indicate a rapid rise of temperature, this epoch, therefore, 

 deserves further attention; there are also fainter indications of an unusual de- 

 pression about May 31, of a constancy between September 13 and 18, and of a 

 rapid decline about Nov. 26. 



The temperatures recorded at the above stations refer nearly to the same period 

 of time, and consequently exhibit many coincidences of departures from regularity 

 which only belong to this period, but as soon as we compare with recorded 

 temperatures covering another period, these coincidences disappear, and it is only 

 by such comparisons of different epochs that we can assure ourselves of the reality 

 or non-reality of any suspected deviation from the regular annual progression. The 

 character of the Salem line is essentially different from that of any of the other 

 lines, its period terminating about the time of the beginning of the others. This 

 is the only station where the record extends, in part, to the past century. 



Examining now, specially, the suspected periods of irregularity they will possess 

 a strong probability of existence if exhibited alike for two independent epochs, for 

 instance, those of the Salem and Providence series. About the beginning of 

 December the march of temperature, at all the stations given, appears to be normal, 

 though there is a remarkable depression about November 26, 27, 28, which latter 

 feature seems to demand further attention. There is no thermal anomaly about 

 the middle of May,^ and the progression about February 12th and in the first and 

 second week of March appears regular enough; at this season, however, the 

 accidental irregularities are very great, and may hide any smaller fixed deviation. 

 The suspected arrest of increasing temperature after May 25 is not supported by 

 the Marietta and Salem observations, and the rise or constancy of temperature noted 



' In an Article on the Yariatious of Temperature at Toronto, Canada (Phil. Trans. Roy. Soc., 

 1853, Vol. 143, part 1), Col. Sabine remarks : " On a reference to Table IV, it is seen that on the 

 average of the twelve years from 1841 to 1852 the 11th of May was 0°.l helow and on the 12th and 

 13th of May respectively 3°.l and 2°.4 above the general mean of the temperature. The meteoro. 

 logical observations at Toronto during these twelve years do not, therefore, support the supposition 

 that the depression of temperature on the 11th, 12th, and 13th of May observed at Berlin (from 

 a series of 86 years of observations) is a general and periodically recurring phenomenon over the 

 whole globe." 



25 March, 1S75. 



