462 



DISCUSSION OF BAROMETRIC OBSERVATIONS. 



verified by leveling from the track of the New London Northern Eail- 

 road, the height thus deduced being 266.5 feet. The readings of the 

 barometer have never been corrected for elevation, but represent the 

 actual pressure at Amherst in inches of mercury at 32° Fahr. 



In regard to the fluctuation of atmospheric pressure, the observations 

 at Amherst may probably be regarded as fairly representative of New 

 England and the adjacent portion of New York. In confirmation of 

 this opinion, the figures at the foot of this page are cited from a pam- 

 phlet of " Meteorological Researches for the use of the Coast Pilot," 

 published in 1877 by the United States Coast Survey. They are the co- 

 eflicients of Bessel's i)eriodic function, under a modified form, in which 

 e-i represents the value which ^p, the time-angle, has at the maximum of 

 the annual inequality, and ^2 is the value of 2^ at the maximum of the 

 semi-annual inequality. The coefficients Bo, Bi, B2 are expressed in mil- 

 limeters. The places named in the first column are all those within the 

 above-named region which are embraced in the tables of the pamphlet 

 (pp. 33, 34). The data from which the numbers in the first seven 

 lines were computed were originally published in 1861 by the Smith- 

 sonian Institution (" Results of Meteorological Observations, 1854-'59") ; 

 those in the seven following lines were derived from the Reports of the 

 Chief Signal Officer, 1872-1876. The latter are reduced to sea-level; 

 the former are not. None of the fourteen are based upon more than six 

 years' observations. The values given separately for Amherst, below the 

 rest, are taken from the present reduction of the twenty-five-year series, 

 and it will be seeu that except in the value of £2 they agree well with the 

 mean of all the others. This angle £2 appears from the given values to 

 be very variable when a comparison is made of different places, or even 

 of the same place in diiferent short series of years, a circumstance, 

 doubtless, connected with the fact that, as apjiears from the present 

 reduction of the Amherst observations, the coefficient B2 of the term 

 B2 cos {2(p — ^2) is less than that of the following term in 3^ ,— of which 

 term no account is made in the pamphlet. 



Place. 



Bi 



Steaben, Me 



Gardiner, Me 



Nantucket, Mass . . . 

 New Bedford, Mass 



Amherst, Mass 



Burlington, Vt 



Rochester, N. Y 



Portland, Me 



Boston, Mass . . . 



New London, Conn. 



Burlington, Vt 



New York, N. Y . . . 



Oawego, N. Y 



Rochester, N. Y 



Mean of the above 

 Amherst, Mass 



mm. 

 759.6 

 757.0 

 761.6 

 759.5 

 755.1 

 751.9 

 746.7 

 761. 2 

 761.8 

 762.5 

 761.5 

 762.7 

 761.7 

 761.2 



mm. 

 1.1 



1.2 

 1.0 

 1.1 

 1.6 

 1.1 

 0.9 

 0.4 

 0.9 

 1.0 

 1.6 

 1.3 

 0.9 

 1.2 



mm. 



0.7 

 0.5 

 0.6 

 0.7 

 0.3 

 0.6 

 0.6 

 0.4 

 0.4 

 0.3 

 0.3 

 0.4 

 0.5 

 0.4 



265 

 290 

 289 

 277 

 355 

 261 

 354 

 297 

 308 

 323 

 329 

 339 

 343 

 340 



1.1 

 1.2 



0.5 

 0.5 



312° 9' 

 308° 57' 



19 

 350 

 40 

 51 

 53 

 30 

 51 

 56 

 44 

 63 

 58 

 49 

 94 

 320 



39° 9* 

 82° ZC 



