The group then set about performing very careful and extensive experiments of the acceleration due to gravity, g, in the mines using calibrated "half-second pendulums" at various locations around the mine.* The work was a collaboration with John F. Hayford, Inspector of Geodetic Work at the (U.S.) Office of the Coast and Geodetic Survey. McNair's principle motivation was to use the small variations in g to aid in determining an improved value for the density of the Earth and, of course, to ultimately use the technique to find ore deposits. Extensive measurements were made, sent to the Geodetic Survey for analysis, and after considerable delay the corrected values of g for the first measurements were returned. A fractional increase in g with depth of 7.7 × 10^-5 per km was found. Based on a simple analysis, a decrease was expected. McNair was still questioning the calibration of the pendulums, shipped from Washington D.C., almost 10 years later, and was apparently concerned about the increase in g with depth they observed. He received reassurance from Hayford in 1911 (then in Evanston) that the calibration simply could not have been that far off. Nevertheless, after the press the group received for their previous measurements, it is understandable that they were reluctant to publish any additional controversial results. This was unfortunate since their results could have provided some of the earliest evidence for Earth's very dense core had they been published.**

Any relationship between the values of g obtained and the various local geological formations was never determined. According to Fisher, this would "involve a great amount of computation, promised by the U.S. Coast and Geodetic Survey" which apparently was never carried out.

Shortly after these experiments Osborne left to begin a long and successful career at the Bureau of Standards in recognition of which he would later return to receive an honorary Doctorate.

The Engineering Education Years

When the School started, of course, the Physics Department was only to provide a fundamental background in physical science considered essential for mining engineers. Over the first few decades of the School's existence this would also include specialists in chemical and metallurgical engineering. From about 1900 until 1930 the Physics courses centered on the five introductory physics courses, B1 to B5, and the two engineering mechanics courses, C1 and C2.

* They used Mendenhall 1/2-second pendulums capable of detecting relative changes in g of about 1 ppm (~ 1 milligal). By definition a half-second pendulum takes one second for a full swing. A summary of the experiments is in the 21 Sept 1902 issue of the Sunday Mining Gazette.

** Their result is comparable to modern world-wide averages inferred from other types of Earth density measurements. For example refer to the "Preliminary Reference Earth Model" put forward by Dziewonski and Anderson in 1981.

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