I understand fully the method of calculating the depth of water beneath the surface. What you wish to know is, after the substance is shown to exist beneath a certain point, whether it be mineral, metal or water, and the kind, character and description of each. As you are aware of the fact, the simple "forked rod" will indicate the presence of either of these. Now, to tell which of these it is, and the character of the same; if it be water, the kind of water. This is my method of testing the same, whether it be water, mineral or metal: It is on the principle of _affinity_--the attraction that like substances have for each other. After the rod indicates the particular spot, I take a sponge and saturate it with ordinary drinking water, either from spring or well, and put it on the top of the rod, and test it with this. If the substance beneath be water, and the same kind of that in the sponge, it will turn much stronger, and the demonstration be more active and powerful. But, if the rod should not turn at all, it will be some other substance, either mineral or metal. To test the kind of water, after I am satisfied that it is water--to discover, for instance, whether it be sulphur water, I dip my sponge in that kind of water, and test as above. If the movement of the rod be active and strong when this is done, the water below will be that species of water. If salt water, dip the sponge in that kind of water, and the result will be similar; and so on through the whole catalogue of waters. In regard to the metals. The tests are made in a similar manner. After I discover by proper tests that it is a metal, which are as follows: If it be metal or mineral, after the sponge is saturated with water, the rod will not act at all. I then put a piece of metal on the top of the rod; first, a small bit of iron. If there is no movement of the rod at the spot already indicated, it is safe to conclude that the substance is not of that nature; so I continue the experiment with different kinds of metal--lead, silver, copper, tin, gold, etc., until I find some one of these that will cause the rod to turn and operate in a manner sufficiently strong and satisfactory. The same method pertains to the minerals. Of course, a great deal of the practical operations of these various tests, will depend upon one's discretion and judgment at the time they are made, which it is impossible to put upon paper. This is but a general outline of the system. If I can be of any further assistance to you in the investigation of this subject, do not fail to let me know of it. Would be pleased to hear from you at any and all times. Be sure and send me your pamphlet. Yours, respectfully, HARRY SANGSTER.