The MacLagan Penetrometer (ca. 1910 - 1915) |
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| Penetrometers are used to determine the optimal exposure settings for performing an x-ray of a particular part of the body. They typically consist of a series of metal (usually aluminum) plates of increasing thickness. Sometimes they are arranged in the form of stair steps. | |
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| This particular unit, the MacLagan Penetrometer, was manufactured by the McIntosh Electrical Company, or as it was later known, the McIntosh Battery and Optical Company of Chicago. I am not sure when the firm changed its name, other than that it was done by 1912. McIntosh seems to have gotten into the x-ray business by producing static high voltage machines. The Hogan Silent XRay Transformer, referred to on the plate (below left), was a featured product in their 1912 catalog. | |
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The penetrometer contains ten metal disks arranged on the inside like the numbers of a clock, and each disk has a number cut through it so that it shows up on an x-ray image (photo above right). According to the plate, the number indicates that a particular disk corresponds to so many inches of solid tissue. As such, the images of the various disks on a test x-ray would indicate the appearance of body parts that correspond to the indicated thickness. X-ray image courtesy of David Allard References: Grigg, E.R.N. The Trail of the Invisible Light. Charles C Thomas 1965. pages 51 and 634. |
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