Johnson Road Project Silver Creek Ranch

Here are some thoughts on two parts of the description; Goddard's determined elevation, and the "gulch."

Goddard's determinations of the altitudes are in error. However, his observation of 23.38"hg is apparently very good--it should mathematically reduce to 6,738', which is a near fit to the general area, as the elevation of where the bridge crosses Lyons Creek is 6,672' and Wilson Ranch is 6,610'. See below for details of these barometric determinations.

	From Google Earth, the gulch (ravine) leading down to Fred's Place. The pushpin marked bridge is the bridge crossing Lyon's Cr at the meadow. Where the highway route sign is is Freds. Unfortunately, at this time there is not high resolution imagery available for this area. It would be like Goddard to mention this topographical feature (ravine, "gulch"), because the road, quite naturally, avoids entering it.
	An overlay of topo and photo using TerraBrowser images sourced from Teraserver. Shown are Wilson Ranch, the meadow where the bridge crosses Lyons Cr., the wide turnout at Freds immediately below, and the slide that took out the Wrights Lake Road a few years ago. Note again the ravine heading on Lyons Creek and leading down to Freds.
	An image rendered from USGS DEM (Digital Elevation Model) files. Nice view of the "gulch" and the crest between the S. Fk and the valley of Silver Creek.
	A topo image and a satellite image of the bridge and meadow.

An examination of Goddard's reported elevations in the area of the present study of the Johnson Wagon Road.

Here are tables showing Goddard's barometric observations taken along the route of the Johnson Cut-off in 1855. This was early use of the aneroid barometer, and Goddard was uncertain of the appropriate mathematical reductions and temperature compensation to give the altitude. But, the aneroid of this form was only invented by Vidi [Vidie] in Paris in 1845, so this was still brand new technology in 1854. Very early use in a survey!

Goddard's instrument was marked "No. 264, J. W. Queen, Chesnut Street, Philidelphia." Queen. In the 1850s, Queen's anerouids were actually supplied by W. & L. E. Gurley in New York, who probably imported them for him from Vidi in Paris or Dent in London.

Aneroids, a calibrated mechanical instrument, are useful because of their portability, but are never intended to be used without reference to a standard direct-reading mercury barometer. Goddard did make these references with a mountain (ie, portable) iron cistern mercury barometer by Henry & James Green to set his aneroid (Placerville) at the beginning of his work, but constant problems with the fragile mercury barometer eventually rendered it useless, so all observations were made with the aneroid. He was, however, very careful of the instrument--carrying it only on foot on a cushion in a basket in an effort to have it maintain its zero.

In following Goddard's narrative, he gives his determined elevation for many places on the Johnson Road curriently under study. But these reported elevations at known locations are found to be in error, and are therefore not very useful in attempting to locate unknown locations.

But in Goddard's tables of Meteorological Observations are given the original observations of his instrument for each location in "hg (inches of mercury). This remains Good Data. It is only necessary to take the original data and reduce it mathematically by modern method to get a more accurate determination of the actual elevations.

Bear in mind, that not knowing what the sea level barometer was reading on any particular day in question in 1855, it is necessary to use an accepted seasonal daily mean pressure. So this does not take into account weather variations which would have affected his barometer. However, the registers over the corresponding days kept by Dr. Logan in Sacramento and Mr. Lelner at Coloma slow very little variation from a standard mean.
However, the temperature of Godard's instrument (which was not temperature compensated) can have a larger effect than the daily barometric variation.

Goddard: "There is indeed much uncertainty as to the amount of correction the aneroid requires for differences in temperature, and indeed as to what formula is the most applicable to the reductions of observations made with this instrument. After trying several, I found the well known formula of Baily For. 38 Astro Table to give the best result, and therefore have used it in all cases. "

Note: I have located the formula and tables by Baily that Goddard used in Smithsonian Meteorological Tables [Based on Guyot's Meteorological and Physical Tables], Smithsonian Miscellaneous Collections No.1032. I should have a copy of the 1893 second edition in hand in the near future.

The formula I have used is a simple isothermal calibration standard from the Bureau of Standards.
Z= 62900 log₁₀ P_o/P
where Z=altitude in feet, P=Pressure at the upper limit in any units, and P_o=pressure in same units as above corresponding to zero altitude.
It makes assumptions for the temperature of the column of air then that we cannot know.

Place	Goddard's barometer observations 1855	Goddard's own reduction to altitude	Modern reduction to altitude from Goddard's observations	Actual Elevation
Johnson Pass	22.84"hg	6,752'	7,376'	7,377'
Strawberry	24.12"hg	5,136'	5,886'	5,900'
Wrights Lake Rd	24.50"hg	4,901'	5,459'	5,427'
Silver Cr. Ranch	23.38"hg	6,177'	6,738'
Divide bet. S. Fk and Silver Cr.	23.27"hg	6,277'	6,866'	This ridge follows along at approx. 6,800'
Peavine Hill	23.39"hg	6,410'	6,726	6,645'
Brockless Trading Post	24.34"hg		5,638'
Bartlett's Br.	26.75"hg	2,532'	3,059'	3,000'

Aneroid instruments are calibrated in "hg, but often have a scale of elevation in feet/meters. The elevation scale is only approximate, and is useful between stations. Some modern units designed for hikers are calibrated only in feet/meters. One can set the indicator to correspond with a place of known elevation, such as a contour on a topo map, and navigate to a place on another contour. Accurate estimates actually require that observations of pressure and temperature are made at both upper and lower stations and are then reduced using log tables. But the moveable scale (stem setting) on mine--an early 20th C instrument by Short & Mason, was designed by mid 19C Astronomer Royal, Professor G. B. Airy and is much more useful.

In using Airy's scale, 0' is always set to 31"

The formula used is then D = (H-h) (1 + [T+t-100] / 1000)

D being the distance between upper (H) and lower (t) stations in inches, and T/t is the temperature at upper/lower stations in Fahrenheit.

This is how Goddard's elevations were done--the elevation of each station was based on the previous station and all stations eventually added together. The elevation of Placerville, from multiple observations of the mercury barometer, was the referenced base.

But calculating elevations from Goddard's observations isn't even necessary to follow him.
The next time I am in the area of these readings, I intend to bring my own pocket aneroid. By setting it to correspond to Goddard's stations, it should give the corresponding reading at the others--this would be purely comparative--no necessity to reduce to altitude.

Read the follow-up

Before GPS, I used to carry a modern Swiss made altimeter by Thommen. It's scale has 20' increments to 15,000'--this resolution requires a gear train so that the indicator revolves five times covering the range. But I soon stopped using it when I found that that the action of snapping/unsnapping the deluxe leather carrying case could cause an indicated elevation change of 100 feet or more.
Too much mechanism and false precision. My weighty old Short and Mason scale that has scale divisions in 50' divisions is much more robust and, with reasonable care, holds its zero!

Bob Graham

Some notes.

Goddard's essay on his use of the barometer in his surveys--very early use of the aneroid on surveys.

The history of Day and Goddard's surveys excerpted from From Trails to Freeways.

The Mountain Barometer

How modern mathematical reduction of historical barometric observations can identify disputed sites.

An overview of 19th Century barometric determinations of altitude.

Lt. R. S. Williamson's essay on The Use of the BArometer on Surveys and Reconnaissances--ground breaking work conducted in the Sierra Nevada in the 1860s. This is online, and difficult to access, but contains much historical data of great importance to climatologists.