World-life; or, Comparative geology . 22) tobe so situated in respect to B, that its longer diametera h, makes an oblique angle with the line A B, joining thecentres of gravity of the two nebulae. One extremity ofthe mass, as at b^ will experience a greater relative attrac-tion toward B than the other extremity of the mass will experience; and thisinequality will con-tinue as long as theangle B A 6 is not aright angle, and, inthe case supposed, aslong as B A ^ is lessthan a right effect must be toturn the nebula A insuch direction that itslonger diameter pro-duced will tend topass th
World-life; or, Comparative geology . 22) tobe so situated in respect to B, that its longer diametera h, makes an oblique angle with the line A B, joining thecentres of gravity of the two nebulae. One extremity ofthe mass, as at b^ will experience a greater relative attrac-tion toward B than the other extremity of the mass will experience; and thisinequality will con-tinue as long as theangle B A 6 is not aright angle, and, inthe case supposed, aslong as B A ^ is lessthan a right effect must be toturn the nebula A insuch direction that itslonger diameter pro-duced will tend topass through the cen-tre of gravity of in the meantime,B and A may havetravelled to widelyseparated regions ofspace. The rotationbegun in A will there-fore Continue unhin-dered. It will continue in any case where the hinderingaction of B is less than the action which inaugurated therotation; as for instance when the form of A becomesmore svmmetrical, though the action of B should bereversed by change of position, without being less.*. Fig 22. Rotation Resulting WithoutActual Impact. * A modern writer of much sagacity has maintained that an amorphousnebula would be made to rotate by the tangential action of currents of nebulous N^EBULAR ROTATION. 09 2. Causes of JVehdar Forms.—As to the spiral formof nebulae different sug-gestions may be made. We may,for instance, conceive it as arising from the action of aresisting medium in space. This would develop a retarda-tion in the peripheral portions, and would explain thetendency of parts to be left behind, as indicated in certainfeatures of spiral nebulse. Other phenomena would beexplained on the suppc-sition of some translation througha resisting medium. The unequal actions resulting froma non-homogeneous constitution of the nebula would favorthe production of a spiral form. Professor Daniel Kirkwood has offered the followingsuggestion on this subject: The tendency in a rotatingnebula, to unequal angular velocities, resulting from t
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