I can find no fault with the authors' opening words.
I have always observed that when any novelty is presented for the consideration of man, which is not readily proven by already well known scientific laws, or which may not be demonstrated by the knowledge and power of most persons, it is found extremely difficult, if not impossible, to gain the attention of the devotee of science. Whether, indeed, it be from lack of interest, from incredulity, or from the fear of ridicule, or from any other cause, we look with distrust upon anything which is not in harmony with our preconceived ideas or theories, and we are apt to raise the cry of humbug or superstition, and reject, with a contemptuous assumption of superiority as unbelievers, propositions which properly put to the test might prove of value to mankind.
Happily for us a wise Providence has not ordained that all minds shall plough in a single furrow of the great field of knowledge. Some, therefore, believe nothing but what they see, and frequently doubt the evidence of their own senses. Others believe everything they see and nearly everything they hear, and seize with too great credulity upon every new thing presented to them. There are others who disbelieve nothing that is presented to them, however apocryphal, without full and impartial investigation, aided not by testimony alone, but by actual demonstration. Again, there are men who are afraid to investigate, lest the world should call them visionary; these are always prepared to apologize for examining anything outside the mere routine of their special science. But the most frequent error of mankind is to doubt and ridicule, without investigation, everything which is not commonly received. To such I would cite the pungent words of Solomon: "He that answereth a matter before he heareth it, it is a folly and a shame unto him."
He suggests dowsing is an electromagnetic phenomena; I concur. Since water flowing underground must contain some ionised molecules, and it is flowing through the earth's magnetic field, then
by definition it must generate an electromagnetic field. The only questions then are how strong that field is, and what kind of people are the most sensitive to changes in the local field strengths as they move through it.