. The principles of physics. first established in the steelneedle, so that if placed in a horizontal (or any other) position itwill rest in that position. Then it is strongly magnetized. After-ward it will take the horizontal position only at the magneticequator of the earth. Experiment 1. — Place a dipping-needle over the + pole of a barmagnet (Fig. 414). The needle takes a vertical position with its — poledown. Slide the supporting stand along the bar; the — pole gradually rises until the stand reachesN,j fj s igS the middle of the bar, where the needle becomeshorizontal. Continue mov-ing th
. The principles of physics. first established in the steelneedle, so that if placed in a horizontal (or any other) position itwill rest in that position. Then it is strongly magnetized. After-ward it will take the horizontal position only at the magneticequator of the earth. Experiment 1. — Place a dipping-needle over the + pole of a barmagnet (Fig. 414). The needle takes a vertical position with its — poledown. Slide the supporting stand along the bar; the — pole gradually rises until the stand reachesN,j fj s igS the middle of the bar, where the needle becomeshorizontal. Continue mov-ing the stand toward the*jS — pole of the bar; afteryje 414 passing the middle of the bar the + pole begins todip, and the dip increases until the needle reaches the end of the bar,when the needle is again vertical with its -I- pole down. If the same needle be carried northward or southward along theearths surface, it will dip in the same way as it approaches the polarregions, and be horizontal only at or near the MAGNETIC POLES OF THE EAETH. 531 Experiment £. — Support a small pane of window glass on a table, byplacing under the glass near its corners four slices of cork about one-eighth of an inch thick. Be-neath the center of the glasson the table place a circulardisk of magnetized steel. Siftiron turnings upon the upperface of the glass through atine wire sieve. Gently tapthe glass at convenient pointswith the end of a filings arrange themselvesin lines radiating from eachpole. Experiment 3. — Suspenda small magnetized cambricneedle by a fine thread at itscenter and carry it aroundthe disk (Fig. 415). Theneedle passes through all thephases stated in Exp. 1, sothat we may fancy the diskto be the earth, and study therefrom, in a general way, the changesthat the needle undergoes, as it is carried around the earth in a norther-ly or southerly direction.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
