210 



♦ KNOWLEDGE 



[March 13, 1885 



surface. A covered spirit or other lamp is placed on the 

 link O C, and sends a beam of light through a small hole 

 on to the mirror at O. The link A is fixed, and C is 

 revolved about O till A O C is equal to the angle to be 

 trisected. This done, the mirror is revulved till the 

 reflected beam from the lamp passes along A, and 

 it is then clamped firmly to A. It is evident now 

 that if C is moved towards A, the beam and its reflec- 

 tion approach each other also, the latter describing the 

 same angle from O A as C describes from its first posi- 

 tion, which may be supposed to be D. The trisection 

 is eflected when the reflected beam is observed to pass 

 through E ; for then we have angle DOC described by 

 the beam = angle A E described by the reflected beam. 

 But A E = C E by the nature of the rhombus, so that 

 the angle through which O C has been turned is one-third 

 of the given angle. This apparatus is inferior to the pre- 

 ceding in requiring an accurately planed surface and 

 careful mounting for the mirror. 



We see, then, that the problem of the trisection of au 

 angle may be solved in more ways than one by mechanical 

 means, the required instruments consisting only of pivoted 

 rods, with, in one case, the addition of tension to keep 

 three points in a straight line. 



LIFE IX OTHER WORLDS. 



Bv Richard A. Proctor. 



(Continued from p. 1G4.) 



AND while we thus recognise throughout our earth's 

 history as a planet. Nature's ap|iarent purpose of 

 providing infinitely varied forms of life at all times and 

 under the most varied conditions, we also perceive that 

 Nature possesses a power of modifying the different types 

 in accordance with the varying conditions under which 

 they subsist. Without entering here into the vexed ques- 

 tion of the actual extent to which the principle of selection 

 operates, we must admit that it does operate largely, and 

 that it must necessarily cause gradual change of every 

 type of living creature towards the most suitable form. 

 This particular operation of Nature must certainly be 

 regarded as an apparent carrying out of the ]iurpose attri- 

 buted to her, — by our manner of speaking when we say 

 that Nature's one great object is the support of life. If 

 types were unchangeable, life would come to an end upon 

 a globe whose condition is not only not unchangeable, but 

 changes largely in the course of long periods of time. 

 But types of life change, or can change when required, 

 at least as quickly as the surrounding conditions — save in 

 the case of certain catastrophes, which, however, never 

 aflfect any considerable proportion of the earth's surface. 



Nor is it easy to assign any limits to this power of 

 adaptation, though we can scarcely doubt that limits 

 exist. The earth may so change in the course of hun- 

 dreds of thousands of years to come that none of the 

 chief forms of life, animal or vegetable, at present 

 existing, could live even for a single year under the 

 changed conditions of those distant times, while yet 

 the descendants of creatures now living (including man) 

 may be as well fitted to the circumstances around them 

 as the most favoured races of our own time. Still there 

 must be a limit beyond which the change of the earth's 

 conditiiD, whether through the cooling of her own globe or 

 the diminution of the sun's heat, will be such that no con- 

 ceivable modification of the types of life now existing 

 could render life possible. It must not be forgotten that 

 Nature's power of adaptation is known to be finite in 



many cases, and therefore must be presumed to be finite in 



all cases. The very process of selection by which adapti- 

 tion is secured implies the continual failure of preceding 

 adaptations. The struggle for life involves the repeated 

 victory of death. Tlie individuals which perish in the 

 struggle (that i-^, which perish untimely) far outnum'icr 

 those which survive. And what is true of individuals is 

 true of types. Nature is as wasteful of typ€s as she is of 

 life— 



So careful of the type ; bat no, 



From scarped cUff and quarried stone 

 She cries, " a thousand types are gone ; 



T care for nothing, all shall go." 



This is, in truth, what we must believe, if, reasoning 

 by analogy, we pass but one step higher in the scheme 

 of creation. We know that Nature, wasteful of indi- 

 vidual life, is equally wasteful of types of life. Must 

 we not infer that she is no less wasteful of those aggre- 

 gations of types which constitute the populations of 

 worlds ] Watching her operations a few brief minutes, 

 we might (setting experience' aside) suppose her careful 

 of individual life. Watching during a few generations, 

 we should pronounce her careful of the type, though care- 

 less of individual life. But we perceive, when we extend 

 the range of time through which we look, that she is care- 

 less no less of the type than of life. Why should this 

 extension of the range of view be the last we should permit 

 ourselves ? If we pronounce Nature careful of the planetary 

 populations, though careless of the types of life which make 

 up such populations, we are simply declining to take a 

 further step in the course pointed out for us by the 

 teachings of analogy. 



Let us go over the ground afresh. Individual creatures, 

 even the most favoured, perish after a time, though the 

 balance may long oscillate between life and death. Weak, 

 at first, each creature which is to live grows at length to 

 its full strength, not without vicissitudes which threaten 

 its existence. As its life progresses the struggle continues. 

 At one time the causes tending to decay seem to prevail 

 awhile ; at another, those which restore the vital powers. 

 Disease is resisted again and again; at first easily, gradually 

 with greater difficulty, until at length death wins the day. 

 So it is with types or orders of living creatures. A 

 favoured type, weak at first, begins after a while to thrive, 

 and eventually attains its fullest development. But from 

 time to time the type is threatened by dangers. Sui round- 

 ing conditions become less favourable. It ceases to thrive, 

 or, perhaps, passes through successive alternations of dtciy 

 and restoration. At length the time comes when the 

 struggle for existence can manifestly have but one end ; and 

 then, though the type may linger long before it actually 

 disappears, its disappearance is only a question of time. 

 Now, it is true that each type thus flourishing for awhile 

 springs from other types which have disappeared. The 

 favoured types of our age are but varieties of past types. 

 Yet this does not show that types will continue to suc- 

 ceed each other in endless succession. For, if we con- 

 sider the matter rightly, we perceive that the analogue 

 of this circumstance is, in the case of individual life, the 

 succession of living creatures generation after generation. 

 And as we know that each family, however large, dies out 

 in the long ruu unless recruited from without, so we are to 

 infer that the various types jjeopling this earth, since they 

 cannot be recruited from without, must at length die out, 

 though to our conceptions the time necessary for this 

 process may appear infinite. 



To the student of science who recognises the true mean- 

 ing of the doctrine that force can be neither annihilated 

 nor created, it will indeed appear manifest that life must 



