Mount Rainier, a Record of Exploration

by Unknown

For the benefit of those not interested in the scientific details of this report, it may be stated at once that the summit of Mount Rainier, according to Professor McClure's observations, is 14,528 feet above sea level. The altitudes of various sub-stations occupied en route will be found further on. An account of the data, with description of the methods employed in reduction and computation, is given, to indicate the degree of reliance to be placed upon the result.

The principal observation to which this report refers was made by Professor Edgar McClure, of the University of Oregon, on the summit of Mount Rainier, Washington, July 27, 1897, at 4:30 p.m., Pacific standard time. The observation consists of a reading of Green's standard mercurial barometer, No. 1612, together with readings of attached and detached thermometers. It appears that the barometer, which was suspended by a ring at the top, was allowed so to hang until it had assumed the temperature of the surrounding air, before being read; that the sky was clear at the time; and that the place of observation, the highest on the mountain, is designated as Columbia Crest.

The barometric reading, corrected for instrumental error and temperature, was 17.708 inches; the air temperature was 29 degrees Fahrenheit.

Concurrent observations were made at 9:30 a.m. and hourly during the afternoon by the regular observers at Seattle, Portland, Fort Canby, the University of Oregon at Eugene, Roseburg, and one observation at Walla Walla at 5 p.m.

In addition to these, during the week preceding the 27th Professor McClure made numerous observations both of pressure and temperature at various sub-stations in the vicinity of Mount Rainier, and simultaneous observations are furnished from Seattle and Portland.

At the very outset of the work of reduction it was evident that Eugene and Roseburg were under an area of relatively low barometric pressure on the 27th, representing atmospheric conditions that did not prevail in the region of Mount Rainier. I therefore rejected the observations at both these places, using only those at Seattle, Portland, Fort Canby and Walla Walla. The strategic position of these four points will be seen at once by a glance at the map.

The method followed in making the reduction was, in brief, to deduce from the observations at the four base stations surrounding the mountain the actual atmospheric conditions prevailing in the immediate region of the mountain. More specifically, the process consisted in determining the atmospheric pressure and temperature at an imaginary sea level vertically under the mountain, which level I shall subsequently call the "mean base."

In this I was greatly assisted by a careful study of the daily weather charts issued by the government, Mr. Pague having kindly loaned me his official file for July. I thus practically had at my disposal observations from all the important points on the Coast, both before and after the principal observation. With due regard to the position and direction of the isobars, and giving proper weight to the observations at each of the four base stations, I finally deduced 30.130 inches as the value of the pressure at the mean base which best satisfied all the data. It ought to be said, perhaps, that this result does not depend upon my judgment to any appreciable extent, but was legitimately worked out from the observations and isobaric lines.

In determining the mean temperature of the air column extending from the mean base to the summit of the mountain, the observations made by Professor McClure during the previous week in the vicinity were so numerous and well timed as to leave far less than the usual amount of uncertainty. Making due allowance for the moderate elevations of the stations, these observations show clearly that the temperature about the mountain at that time followed that of Seattle very closely, and was also not much different from that of Portland, but departed notably from both the heat of Walla Walla and the low temperature of Fort Canby. Allowing proper weight to these facts, the observations at the base stations, with that of Professor McClure at the summit, gave 49 degrees Fahrenheit as the mean temperature of the air column.

I regard the method of reduction outlined above as possessing decided advantages over any other that could be applied to the problem in hand; especially because it admits of using the isobaric charts with great freedom and effectiveness, thereby increasing the reliability of the result to a marked extent.