The Ascent of Denali (Mount McKinley) Part 7

[5] Ottawa: Thorburn & Abbott, 1913, p. 87.

[6] "Mt. McKinley Region": Alfred H. Brooks, Washington, 1911, p. 25.

CHAPTER VII

THE HEIGHT OF DENALI, WITH A DISCUSSION OF THE READINGS ON THE SUMMIT AND DURING THE ASCENT

The determination of the heights of mountains by triangulation is, of course, the method that in general commends itself to the topographer, though it may be questioned whether the very general use of aneroids for barometric determinations has not thrown this latter means of measuring alt.i.tudes into undeserved discredit when the mercurial barometer is used instead of its convenient but unreliable subst.i.tute.

The alt.i.tude given on the present maps for Denali is the mean of determinations made by triangulation by three different men: Muldrow on the Sus.h.i.tna[7] side in 1898, Raeburn on the Kuskokwim side in 1902, and Porter, from the Yentna country in 1906. In addition, a determination was made by the Coast and Geodetic Survey in 1910, from points near Cook's Inlet. "The work of the Coast Survey," writes Mr. Alfred Brooks, "is more refined than the rough triangulation done by our men; at the same time they were much further away." "It is a curious coincidence,"

he adds, "that the determination made by the Coast Survey was the mean which we had a.s.sumed from our three determinations" (twenty thousand three hundred feet).

[Sidenote: Theodolites and Barometers]

There are, however, two sources of error in the determination of the height of this mountain by triangulation--a general one and a particular one. The general one lies in the difficulty of ascertaining the proper correction to be applied for the refraction of the atmosphere, and the higher the mountain the greater the liability to this error; for not much is positively known about the angle of refraction of the upper regions of the air. The officers of the Trigonometrical Survey of India have published their opinion that the heights of the great peaks of the Himalayas will have to be revised on this account. The report of the Coast Survey's determination of the height of Denali claims a "co-efficient of refraction nearer the truth" than the figure used on a previous occasion; but a very slight difference in this factor will make a considerable difference in the result.

The particular source of error in the case of this mountain lies in the circ.u.mstance that its summit is flat, and there is no culminating point upon which the cross-hairs of the surveying instrument may intersect.

The barometric determination of heights is, of course, not without similar troubles of its own. The tables of alt.i.tudes corresponding to pressures do not agree, Airy's table giving relatively greater alt.i.tudes for very low pressures than the Smithsonian. All such tables as originally calculated are based upon the hypothesis of a temperature and humidity which decrease regularly with the alt.i.tude, and this is not always the case; nor is the "static equilibrium of the atmosphere" which Laplace a.s.sumed always maintained; that is to say an equal difference of pressure does not always correspond to an equal difference of alt.i.tude.

There is, in point of fact, no absolute way to determine alt.i.tude save by running an actual line of levels; all other methods are approximations at best. But there had never been a barometric determination of the height of this mountain made, and it was resolved to attempt it on this expedition.

To this end careful arrangements were made and much labor and trouble undergone. The author carried his standard mercurial mountain barometer to Fort Gibbon on the Yukon in September, 1912, and compared it with the instrument belonging to the Signal Corps of the United States army at that post. A very close agreement was found in the two instruments; the reading of the one, by himself, and of the other, by the sergeant whose regular duty it was to read and record the instrument, being identical to two places of decimals at the same temperature.

[Sidenote: Readings on the Summit]

Arrangements were made with Captain Michel of the Signal Corps at Fort Gibbon, when the expedition started to the mountain in March, 1913, to read the barometer at that post three times a day and record the reading with the reading of the attached thermometer. Acknowledgment is here made of Captain Michel's courtesy and kindness in this essential co-operation. The reading at Fort Gibbon which most nearly synchronizes with the reading on top of the mountain is the one taken at noon on the 7th June. The reading on top of the mountain was made at about 1.50 P. M., so that there was an hour and fifty minutes difference in time.

The weather, however, was set fair, without a cloud in the sky, and had been for more than twelve hours before and remained so for thirty-six hours afterward. It would seem, therefore, that the difference in time is negligible. The reading at Fort Gibbon, a place of an alt.i.tude of three hundred and thirty-four feet above sea-level, at noon on the 7th June, was 29.590 inches with an attached thermometer reading 76.5 F.

The reading on the summit of Denali, at 1.50 P. M. on the same day, was 13.617. The writer is greatly chagrined that he cannot give with the same confidence the reading of the attached thermometer on top of the mountain, but desires to set forth the circ.u.mstances and give the readings in his note-book records.

The note-book gives the air temperature on the summit as 7 F., taken by a standard alcohol minimum thermometer, and it remained constant during the hour and a half we were there. The sun was shining, but a bitter north wind was blowing. But the reading of the thermometer attached to the barometer is recorded as 20 F. I am unable to account for this discrepancy of 13. The mercurial barometer was swung on its tripod inside the instrument tent we had carried to the summit, a rough zero was established, and it was left for twenty minutes or so to adjust itself to conditions before an exact reading was taken. It was my custom throughout the ascent to read and record the thermometer immediately after the barometer was read, but it is almost certain that on this momentous occasion it was not done. Possibly the thermometer was read immediately the instrument was taken out of its leather case and its wooden case and set up, while it yet retained some of the animal heat of the back that had borne it, and the reading was written in the prepared place. Then when the barometer was finally read, no temperature of the attached thermometer was noted. This is the only possible explanation that occurs, and it is very unsatisfactory. It was not until we were down at the base camp again that I looked at the figures, and discovered their difference, and I could not then recall in detail the precise operations on the summit. It is hard to understand, ordinarily, how any man could have recorded the two readings on the same page of the book without noticing their discrepancy, but perhaps the excitement and difficulty of the situation combined to produce what Sir Martin Conway calls "high alt.i.tude stupidity."

[Sidenote: In Exculpation]

It is indeed impossible to convey to the reader who has never found himself circ.u.mstanced as we were an understanding of our perturbation of mind and body upon reaching the summit of the mountain: breathless with excitement--and with the alt.i.tude--hearts afire and feet nigh frozen.

What should be done on top, what first, what next, had been carefully planned and even rehea.r.s.ed, but we were none of us schooled in stoical self-repression to command our emotions completely. Here was the crown of nearly three months' toil--and of all those long years of desire and expectation. It was hard to gather one's wits and resolutely address them to prearranged tasks; hard to secure a sufficient detachment of mind for careful and accurate observations. The sudden outspreading of the great ma.s.s of Denali's Wife immediately below us and in front of us was of itself a surprise that was dramatic and disconcerting; a splendid vision from which it was difficult to withdraw the eyes. We knew, of course, the companion peak was there, but had forgotten all about her, having had no slightest glimpse of her on the whole ascent until at the one stroke she stood completely revealed. Not more dazzling to the eyes of the pasha in the picture was the form of the lovely woman when the slave throws off the draperies that veiled her from head to foot.

Moreover, problems that had been discussed and disputed, questions about the conformation of the mountain and the possibilities of approach to it, were now soluble at a glance and clamored for solution. We held them back and fell at once to our scientific work, denying any gratification of sight until these tasks were performed, yet it is plain that I at least was not proof against the disturbing consciousness of the wonders that waited.

It was bitterly cold, yet my fingers, though numb, were usable when I reached the top; it was in exposing them to manipulate the hypsometrical instruments that they lost all feeling and came nigh freezing. And breathlessness was naturally at its worst; I remember that even the exertion of rising from the p.r.o.ne position it was necessary to a.s.sume to read the barometer brought on a fit of panting.

[Sidenote: Calculations for Alt.i.tude]

With these circ.u.mstances in mind we will resume the discussion of the readings taken on the summit and their bearing upon the alt.i.tude of the mountain. It seems right to disregard the temperature recorded for the attached thermometer, and to use the air temperature, of which there is no doubt, in correcting the barometric reading. So they stand:

Bar. Temp.

13.617 inches 7 F.

The boiling-point thermometer stood at 174.9 F. when the steam was pouring out of the vent.

They stand therefore:

_Gibbon_ (334 feet alt.i.tude) _The Summit of Denali_ Bar. Ther. Bar. Ther.

29.590 76.5 F. 13.617 7 F.

Now, the tables accessible to the writer do not work out their calculations beyond eighteen thousand feet, and he confesses himself too long unused to mathematical labors of any kind for the task of extending them. He was, therefore, constrained to fall back upon the kindness of Mr. Alfred Brooks, the head of the Alaskan Division of the United States Geological Survey, and Mr. Brooks turned over the data to Mr. C. E.

Giffin, topographic engineer of that service, to which gentleman thankful acknowledgment is made for the result that follows.

[Sidenote: Fort Gibbon and Valdez as Bases]

Ignoring a calculation based upon a temperature of 20 F. on the summit, and another based upon a temperature of 13.5 F. on the summit (the mean of the air temperature and that recorded for the attached thermometer) and confining attention to the calculation which takes the air temperature of 7 F. as the proper figure for the correction of the barometer, a result is reached which shows the summit of Denali as twenty-one thousand and eight feet above the sea. It should be added that Mr. Giffin obtained from the United States Weather Bureau the barometric and thermometric readings taken at Valdez on 7th June about the same length of time after our reading on the summit as the reading at Gibbon was before ours. From these readings Mr. Giffin makes the alt.i.tude of the mountain twenty thousand three hundred and seventy-four feet above Valdez, which is ten feet above the sea-level. From this result Mr. Giffin is disposed to question the accuracy of the reading at Gibbon, though the author has no reason to doubt it was properly and carefully made. Valdez is much farther from the summit than Fort Gibbon and is in a different climatic zone. The calculation from the Valdez base should, however, be taken into consideration in making this barometric determination, and the mean of the two results, twenty thousand six hundred and ninety-six feet, or, roundly, _twenty thousand seven hundred feet_, is offered as the contribution of this expedition toward determining the true alt.i.tude of the mountain.

The figures of Mr. Giffin's calculations touching the alt.i.tude of this mountain and also determining the alt.i.tudes of various salient points or stages of the ascent of the mountain are printed below:

DENALI (MOUNT McKINLEY)

USING AIR THERMOMETER READING +7 AND THE READING AT FORT GIBBON FOR SAME DATE

Mount McKinley, barometric reading 13.617 in.

Barometer reduced to standard temperature +.027 " Temp. 7 ------ 13.644 in.

Fort Gibbon, barometric reading 29.590 in.

Barometer reduced to standard temperature -.128 " Temp. 76.5 ------ 29.462 in.

Mount McKinley, corrected barometer 13.644 in. 21,324 ft.

Fort Gibbon, corrected barometer 29.462 " 400 "

------ 20,924 ft.

Mean temperature, 41.7--approximate difference in elevation 20,924 ft. -356 ft.

Lat.i.tude, 64--approximate difference in elevation 20,568 " +15 "

Mean temperature, 41.7--approximate difference in elevation 20,568 " +71 "

Elevation lowest, 400--approximate difference in elevation 20,568 " +20 "

------ Elevation above Fort Gibbon 20,674 ft.

Elevation of Fort Gibbon 334 "

------ _Elevation above sea_ 21,008 ft.

USING THE THERMOMETRIC READING OF 7 AT MOUNT MCKINLEY AND THE U. S. WEATHER BUREAU READING AT VALDEZ FOR SAME DATE

Mount McKinley, barometric reading 13.617 in.

Barometer reduced to standard temperature +.027 " Temp. 7 ------ 13.644 in.

Valdez, barometric reading 29.76 in.

Barometer reduced to standard temperature .068 "

------ 29.692 in. Temp. 54