H. A. Hazen — Air-pressure at High t 





[Communicated by permission of the Chief Signal Officer of the United States 

 Army.] 



IN his tenth paper, published in the number of this Journal 

 for January, 1879, Professor Loomis advanced certain evidence 

 to show that, apparently, the progress of a storm center was much 

 apid at the surface of the earth than at elevations above 

 have been advanced by others for and 

 I theory. It is the purpose of this article to put forth 

 facts which have come to light, and which it is hoped 

 will tend to elucidate the subject. 



Many years ago it was noticed from hourly observations at 

 Zurich and at the summit of the Kigi, that while the morning 

 maximum, in the diurnal range of air-pressure, occurred at the 

 lower station at ten, it did not occur at the summit of the 

 mountain until two P. M. Professor Loomis writes (this Journal, 

 January, 1879, pp. 11 and 12): "Over the United States both 

 the maxima and minima " [of accidental fluctuations] " of atmos- 

 pheric pressure generally occur first near the surface of the 

 earth, and they occur later as we rise above the surface, the 

 retardation amounting to one hour for an elevation of from 

 nine hundred to thirteen hundred feet." He says again (pp. 13 

 and 14): "The diurnal movements of the barometer exhibit a 

 peculiarity similar to that found for the accidental fluctuations. 

 The principal maximum occurs at the base at half past eight, 

 but on the summit it does not occur until noon, being a retard- 

 ation of three and a half hours, which is almost identically the 

 same as we have found by a comparison of the accidental 

 fluctuations." He says further (p. 19): "The low center at 

 the height of Mount Washington sometimes lags behind the 

 low center at the surface of the earth apparently as much as 

 two hundred miles." 



Th ~ 

 the (, 

 1879, 



elevations as shown by his own observa 

 Mr. Strachan in discussing this point as brought ( 

 has shown that, taking the average velocity of 

 as twenty miles per hour, and & retardation of 



each thousand feet of ascent, the axis of the stor 

 be inclined 89 0> 5 to the vertical, or, in other wo 

 parallel with the earth's surface. 



