. The Crystal Falls iron-bearing district of Michigan. Iron ores; Geology; Geology, Stratigraphic; Geology, Stratigraphic. MAGNETIC OHSKRVATIONS. 347 . As 1' moves towM-iI the iiiiiyiietic belt the liorizoiital coinponent ut first increases, nnd with it the westward deflection of the needle. Finally, the niaximuin westward deflection is reached, beyond which tlie needle begins to return; it is evident, therefore, that at this point the horizontal component has reached a maximum value. 3. DEFLECTIONS OF THE DIP NEEDLE. The balanced dip needle (i. e., without index error), in an area of no local
. The Crystal Falls iron-bearing district of Michigan. Iron ores; Geology; Geology, Stratigraphic; Geology, Stratigraphic. MAGNETIC OHSKRVATIONS. 347 . As 1' moves towM-iI the iiiiiyiietic belt the liorizoiital coinponent ut first increases, nnd with it the westward deflection of the needle. Finally, the niaximuin westward deflection is reached, beyond which tlie needle begins to return; it is evident, therefore, that at this point the horizontal component has reached a maximum value. 3. DEFLECTIONS OF THE DIP NEEDLE. The balanced dip needle (i. e., without index error), in an area of no local disturbance, is in equilibrium under the action of two couples, namely, the vertical component of the earth's magnetism and the added weight. When displaced from the position of __ »*-^— equilibrium, the horizontal couple re- stores it. In fig. 17 let PP be a balanced Fig. rceesacingo„ ti,e .n,,«ee<iie. dip needle which has been displaced through the angle a. At the two poles the attraction and repulsion of the earth's magnetism may be resolved into horizontal and vertical components, H and V. Taking moments about C, we have, if «=zO, the needle in equilibrium under the couples, V. 2h — m(/. a = 0, where 2&rrPP, mg^the added weight, and a its distance from the center. If this needle, so balanced, is carried to a station within the influence of a magnetic rock, its dip will be determined by the composition of the new forces with the old. The vertical plane will be that in which the hori- zontal needle points at the same station. The equations above give us a ready means of determining- the angle of dip in terms of all the forces. Suppose the needle finally comes to rest at the angle a with the hori- zontal (the north pole being depressed). Then V,.. 2h . cos a — mga cos a —H^. 26 . sin az=0, . . (2) where H^ and V^ signify the resultants of the horizontal, and vertical com- ponents of the earth's and the local Please note that these images are
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