106 H. A. Ilazen — Air-pressure at High Statio 



for the use of the Coast Pilot, Part II," has advanced the theory 

 that a storm center lags behind at the earth's surface, and. 

 speaking of the apparent contradiction of the researches of Pro- 

 fessor Loomis, says : " These results of Professor Loomis show 

 too much for this hypothesis" [that the axis of a "low" is 

 retarded at elevations], "for they show that there is a similar 

 retai lation of ' is! ab ml I le <ame amount in the times of the 

 maxima and minima of the diurnal changes of barometric 

 pressure at the summits of mountains, and we cannot reasonably 

 explain this by means of cyclones with reclining axes. When 

 we shall have a satisfactory explanation of this retardation in 

 this latter case, we shall probably have one in the other." 



In discussing the probable cause for this retardation, the 

 influence of high winds and of variations in temperature will 

 be considered, and the theory that it can be caused by the lag- 

 ging of the axis of a "low" abandoned as untenable, for this, 

 if for no other reason, that, unless a secondary force acts, it is 

 gly difficult to conceive how any fall of pressure at the 

 summit of a mountain would not make "itself felt at the same 

 time at the base through the superincumbent atmosphere. 



If a strong current of air can produce a depression of the 

 mercurial column of ;i I urometer, as has been shown b}^ using 

 a blower for the air current and an air-tight receiver for the 

 barometer (a condition of things, however, which, it should he 

 be borne in mind, can never occur in nature), then why may 

 not the high wind which nearly always accompanies a storm 

 cause a fall in air-pressure, which shall continue as long as the 

 wind is strong at the summit and some time after the storm 

 center has passed the base? 



It is exc Qta be made 



under natural conditions, directly testing the inilnence or non- 

 influence of high winds on the' indications of the barometer. 

 In the absence of such experiments we may indirectly ascertain 

 such influence by comparing observations made at the same 

 moment of time at the summit and base of mountains. The 

 materials for such comparison exist in manuscript copies of 

 hourly observations at the base and summit of Mount Wash- 

 ington during May, 1872. which i have been allowed to consult 

 through the kindness of the Chief Signal Officer of the Army; 

 and in the hourly observations of May and June. 1873, made 

 at the same stations. The latter have been published in the 

 annual report of the Chief Signal Officer for 1873. These 

 stations lie three miles apart in a horizontal direction, and 

 hence we may compute with a near approach to accuracy, from 

 the observations for pressure and temperature, the difference of 

 level between them, by the use of Guvot's hypsometric formula. 



