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 for6 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 fora 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 ec oinever has a glass cistern, and tube of ;‘,ths of an inch 
diameter, the scale for which was adjusted at a pressure of 
thirty uirhes and temperature of 68° F’.; capacity of the tube to 
cistern ,;',; and the instrument is fitted | up in a basernent room, 
the idiben being less than ten feet above the mean level of the 
tide in New York harbor. 
Through the kindness of Lient. 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 isto be deducted from the above general 
mean, it will give for the mean annual pressure at New York, 
30.086 inches; or, if the mean of the hours of 6 and 10 P. M. be 
ay we have ages in. This is without any correction for 
empere The mean temperature of the instrument for the 
entire petiod is sopposed to be about 68° Fahrenheit. 
