This is an excursion into a hitherto unoccupied field, and is offered merely as a series of careful observations, subject to correction by fuller and repeated investigations. The articles are reprinted from the Theosophist, and in a few cases on the early pages, as on page 15, the reference to the pages of the magazine was unfortunately not corrected. We should be much obliged, if any errors are noted in the text or diagrams, that they should be forwarded to Adyar, in order that they may be corrected, should a new edition of the book be required* On page 28, line 8, for helium read occultum.