112 H. A. Hazen — Air-pressure at High Stations. 



summit of Mount Washington is 3590 feet, and between Pike's 

 Peak and Colorado Springs it is 8100 feet. 



The figures in this table, in the fifth and sixth columns, were 

 taken from Professor Loomis' tenth paper; the remaining 

 columns I have computed from the original observations. 

 Unfortunately the hourly observations of 1872 and 74 were 

 continued only during the day hours ; they, however, give 

 satisfactory results for the principal morning maximum and 

 afternoon minimum. A marked peculiarity will be noticed 

 in column two in the means of the observations for seven and 

 eight A. M., namely : a steady fall during these hours. This is 

 due not to natural causes at all, but to the fact that at the mid- 

 night observation the barometer was pushed into its case and 

 locked up. In this position the temperature indicated by the 

 attached thermometer was lower than that of the room, con- 

 sequently, by the time of the second observation the next 

 morning, after the barometer had been suspended for an hour 

 in the room, the temperature of the air in the room would be 

 indicated by the attached thermometer, while the mercury and 

 scale of the barometer would change their temperature much 

 more slowly, and the correction for temperature being too great, 

 the readings of the barometer were made too small, until the 

 different parts of the lined a common tem- 



perature. The attached thermometer at the base indicates that 

 the observations there were not made in the living room, or else 

 ire in the room was very low. (See note at foot of 

 Table III.) It will be noticed that in each case after the 

 morning maximum of pressure was reached at the base, the 

 mean temperature of the air column was rising, and in con- 

 sequence, the pressure did not begin to fall at the summit 

 till some time had elapsed. For the afternoon minimum a 

 reverse of the conditions and effects is noticeable. One inter- 

 esting circumstance should not be overlooked : while at Mount 

 ton the lagging in the morning was three hours and a 

 3590 feet, or one hour to each thousand feet, at Pike's 

 Peak it was only two hours for 8100 feet, or one hour to 4000 

 feet. This is due in part to the fact that after the morning 

 maximum the fall in pressure was much more rapid at the 

 lower western station than at the eastern, and this counterbal- 

 anced the rise in pressure at the summit due to the increase of 

 temperature. 



Again, we see that in the single case wc have of observations 

 through the night, there is little or no retardation in the morning 

 minimum 0l This is precisely what we 



this nme the temper- 

 ature changes only slightly, tho can be laid 

 upon this because the oscillation is correspondingly small. 



