* 
10 £. Loomis— Reduction of Barometric Observations. — 
In some cases, an appreciable error may arise from assuming 
that the pressure at sea-level under Mt. Washington is given by 
the formula $(2B+8P) and a more accurate value may be 
derived from the isobars drawn to represent all the observations 
in the vicinity of Mt. Washington. Column tenth shows the 
height of the barometer at sea-level under Mt. Washington 
obtained by this method. ese numbers were generally 
obtained from the isobars drawn on the Signal Service maps, 
but in a few of the cases I have made a slight change in the 
position of the isobars when the curves on the Signal Service 
maps did not appear to have been. drawn with sufficient care. 
Column eleventh shows the differences between the numbers in 
columns three and ten. The average of the numbers in-column 
eleventh is 0°34 inch. The error in the assumed mean temper- 
ature of the air column produces a small effect, but by none of 
the preceding refinements are the discrepancies to be explained 
materially changed. 
In order to have a graphic representation of the relation of 
these quantities to the state of the barometer, I have 
curves representing the barometric observations on Mt. Wash- 
ington, and also the curves of pressure at sea-level, for the entire 
period of the three years which comprehend the observations in 
tables I and IT; and on these curves I have indicated by 
small black circles, the position of each of -the forty cases inclu- 
ded in table V. The accompanying chart, plate 1, shows such 
portion of these curves as embrace the cases enumerated. The 
ut had not yet reached the point of mean pressure. ' Of the 
remaining five cases, two occurred at a secondary minimum; 
t sea-level, and the remaining case coincided with a 
slight secondary minimum. 
Were these cases of low pressure on Mt. Washington accom- 
anied by a cyclonic movement of the winds? In order to 
i pt 
_ decide this question I have examined the direction and veloc- 
ER ee ea Pe eG RAGE eT Teg Ne ea 
