"A Textbook of Theosophy" is a small book written by C. W. Leadbeater. I actually have a copy of this 1914 edition, published in Adyar, Madras, India. A plethora of other editions exist, indicating that we are dealing with a fairly popular text.
I admit that this *is* the best introduction to Theosophy I've read, at least Theosophy as understood by the Adyar-based branch of Theosophy. (After the death of founder Blavatsky, the Theosophical Society split in two main factions, often referred to as "Adyar" and "Pasadena" after their respective places of domicile.) To those bewildered by Blavatsky's magnum opus "The Secret Doctrine" or the Pasadena group's "Fundamentals of the Esoteric Philosophy", I heartily recommend Leadbeater's more popularized overview.
There really isn't much to say about "A Textbook of Theosophy". All the basic teachings of this new religious movement are included: cosmic evolution, astral bodies and astral worlds, reincarnation, ascended masters... The author even makes a valiant attempt to explain "the planetary chains" and "root-races". For some reason, the book doesn't mention the coming World Teacher, Jiddu Krishnamurti.
I admit that Leadbeater sounds convincing, perhaps because we heard it all before (subconsciously or otherwise). After all, Theosophy, with its combination of progressive evolution and "Eastern" religion, is the matrix for much of the New Age. It's fascinating that "A Textbook of Theosophy" sounds pretty old hat today, when a century ago it was presumably its exotism that drew adherents.
But is it true? Well, I admit that Leadbeater lost me when starting to exposit on the planetary chains...