Identifier: dentaloral00mcco (find matches)
Title: Dental and oral radiography : a text book for students and practitioners of dentistry
Year: 1916 (1910s)
Authors: McCoy, James David
Subjects: Radiography, Dental X-rays Teeth Mouth
Publisher: St. Louis : Mosby
Contributing Library: West Virginia University Libraries
Digitizing Sponsor: LYRASIS Members and Sloan Foundation

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and with-drawing it. The filings will cling to it in greatnumbers, as they will likewise do to the other endof the same magnet if it too be placed in thefilings. The middle of the magnet (or that por-tion midway between the two poles) however,does not possess this property, but as the endsare approached the attraction increases, until thepoles are reached where the attraction reachesthe maximum. In observing the action of the two poles of amagnet in attracting the iron filings, no particu-lar difference is observed. They both attract theiron filings. There is a difference, however, which 34 DENTAL AND ORAL RADIOGRAPHY may be shown by experimenting with two mag-nets, one of which should be suspended at its cen-ter like an ordinary compass, while the other isheld in the hand. If the north pole of the mag-net held in the hand is moved near the north poleof the suspended magnet they will repel eachother. Likewise if their south poles are ap-proached they will repel each other. But if the
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Fig. 5. The action of iron filings in forming definite curved lines about an ordinary bar magnet indicates that the magnetic field exerts its influence in certain definite directions which are called the magnetic lines offorce. north pole of one be placed near the south poleof the other they will attract each other. Thisshows that like poles repel each other, ivhile un-like poles attract each other. The space surrounding a magnet which is sub-ject to its influence is known as its magnetic field.The presence of this magnetic field is easily dem- MAGNETISM 35 onstrated by placing a magnet under a sheet ofpaper upon which iron filings have been evenlyspread. By tapping the paper lightly, the filingswill form into a series of curved lines extendingfrom one pole of the magnet to the other pole, asillustrated in Fig. 5. The formation of these def-inite curves indicates that the magnetic field ex-erts its influence in certain definite directionswhich are called the lines of magnetic force. K

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