326 Synopsis of a Meteorological Journal. 



the year. This effect appears to be due to the proximity of sev- 

 eral violent storms of wind which passed over neighboring regions 

 during the month, but did not visit New York. The mean for 

 December of this year, is uncommonly low, and it is believed to 

 be due to the dispersive effect exerted upon the atmosphere by 

 the several violent and extensive storms which passed over us 

 during the month. 



The means of the several daily observations for seven years, 

 show an excess in those assigned to 10 A. M. ; also, a probable 

 disproportion in those for 6 A. M. The former is probably owing 

 chiefly to the fact that the observations for that hour, in most 

 cases, are necessarily anticipated, and approximate more nearly to 

 9 A. M., and are taken at or near the time of the daily maximum 

 of elevation ; while the latter are perhaps slightly increased by 

 the fact that for a portion of the year the hour assigned is too 

 early for convenient observation. It is not improbable, that the 

 mean of the two observations at 6 P. M. and 10 P. M., gives more 

 nearly the true average pressure for the whole term of years, being 

 30.097; while the general mean in the table is 30.101. 



My barometer has a glass cistern, and tube of y^ ths of an inch 

 diameter, the scale for which was adjusted at a pressure of 

 thirty inches and temperature of 68° F. ; capacity of the tube to 

 cistern ^\ ; and the instrument is fitted up in a basement room, 

 the cistern being less than ten feet above the mean level of the 

 tide in New York harbor. 



Through the kindness of Lieut. Riddell, R. A., the officer in 

 charge of the new magnetic observatory in Canada, I had an op- 

 portunity, in September last, of comparing the adjustment of my 

 barometer with one of Newman's portable iron-cisterned barome- 

 ters, sent as a standard of comparison from the Royal Society. 

 This comparison, made at the temperature of 59° F., showed an 

 excess of 0.015 in. in my barometer, over that of the Royal Soci- 

 ety. This agrees nearly with my own admeasurement ; but I 

 had allowed the excess as compensation for the capillarity of the 

 tube, in order to avoid the necessity for this correction. If, how- 

 ever, this difference is to be deducted from the above general 

 mean, it will give for the mean annual pressure at New York, 

 30.086 i^iches ; or, if the mean of the hours of 6 and 10 P. M. be 

 taken, we have 30.082 in. This is without any correction for 

 temperature. The mean temperature of the instrument for the 

 entire period is supposed to be about 68° Fahrenheit. 



