This pamphlet responds to the increasing demand for exact dosimetry in the administration of roentgen rays. The introductory chapters expound the principles of dosimetry, discussing the measuring of the total of roentgen rays produced, the laws governing the absorption of rays, and their dispersion. The differential points between surface and intensity in the deeper parts of the object irradiated are clearly presented. Explanations of the use of the tabulated items are attached to the numerical tables. The tables proper permit of a rapid calculation of the quantities and intensity of the rays to be applied.