Archive image from page 266 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana0402todd Year: 1849 K to L in order to produce this motion : half of it might be wood, bone, or iron, provided the other half retained its elastic power. The effect would be the same, and the bar A B at N would be elevated by the tension between T L, Fig. 689. connecting the fixed point K with L by the rigid body K T. It is the omission of the fulcrum K, in calculating such oblique forces, which has hitherto obscured the explanation of the intercostal muscles. This may be i
Archive image from page 266 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana0402todd Year: 1849 K to L in order to produce this motion : half of it might be wood, bone, or iron, provided the other half retained its elastic power. The effect would be the same, and the bar A B at N would be elevated by the tension between T L, Fig. 689. connecting the fixed point K with L by the rigid body K T. It is the omission of the fulcrum K, in calculating such oblique forces, which has hitherto obscured the explanation of the intercostal muscles. This may be illustrated in another way (fig. 690.). Let AB and c D represent bars as before upon A c ; t' the tension ; let c D and A c be fixed ; withdraw the pin at A, and the bar A B is drawn fonvards into the position B', and the tension t becomes perpendicular to the two bars. On the other hand, reverse the experiment, as in Jig. 691.; supposing c D and the perpendicular body c A fixed, withdraw the pin at A, and the bar A B is drawn backwards to B'. This presupposes the bars kept apart, Fig. 690. B' otherwise the free bar would approximate the fixed bare D. Therefore, one fulcrum is pushed upon by one bar, and pulled upon by the other. If the bars were kept fixed, and the body re- presenting the spine was left free, the tension would draw this last mentioned body into the Fis. 691. t B; position of c c and cf c'fig. 678. Therefore, the element of the two fulcra is the chief agent for directing their upward or downward move- ment, under an oblique tension. If we arrange two bars with one fulcrum {fig. 692.), and allow Fig. 692. a £ the tension to act as before, then the effect is only to draw the two bars together, as o b and o' d(fig. 693.). If we have an arrange- ment to substitute two fulcra at a a'fig. 692. and withdraw the centre fulcrum, then the two bars rise as before. Fig. 693.
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