June 23, 1898] 



NATURE 



85 



almost equal to the initial velocity of rotation, in order that it 

 may be exactly equal to the mean velocity of rotation. A strict 

 equality being no longer necessary, the paradox does not exist 

 any more. The explanation is nevertheless incomplete. What 

 is the reason of this approximate equality, of which the 

 probability is no longer zero, it is true, but still very small? 

 And, especially, why does not the moon undergo slight 

 oscillations about its position of equilibrium (if we eliminate, 

 of course, its numerous librations, due to other well-known 

 causes) ? These oscillations must originally have existed ; they 

 must have become extinct by a kind of friction, and everything 

 tends to make us believe that the mechanism of this friction is 

 that which I have just analysed with respect to the ocean tides. 

 When the moon was not yet solid, and formed a fluid in the 

 form of a spheroid, this spheroid must have experienced enor- 

 mous tides, by reason of the proximity of the earth and of its 

 mass. These tides could only have ceased when the oscillations 

 became almost entirely extinct. 



It seems that Jupiter's satellites, and the two planets nearest 

 the sun, Mercury and Venus, have also a rotation, the duration 

 of which is the same as that of their revolution ; it is doubtless 

 for the same reason. 



It might be thought that this tidal action has no connection 

 with our subject. I have as yet only spoken of rotations, and 

 in the studies relative to the stability of the solar system the 

 movements of translation are only dealt with ; but a little 

 attention shows that the same action makes itself equally felt on 

 :ie latter. 



We have just seen that the attraction of the moon on the earth 

 'ioes not act exactly through the centre of the earth. The 

 attraction of the earth on the moon, which is equal 

 and exactly opposite, would not pass either through this 

 centre ; that is to say, through the focus of the lunar orbit. 

 A disturbing force is the result, very small in reality, but 

 sufficient to make the moon increase in energy. The active 

 force of translation thus gained by the moon is evidently smaller 

 than that of rotation, lost by the earth ; because a part of the 

 energy must be transformed into heat in consequence of the 

 friction engendered by the tides. The period of revolution of 

 the moon lasting about twenty-eight sidereal days, a very simple 

 calculation shows that this body gains twenty-eight times less 

 vis viva than the earth loses. 



I have already explained the action of a resisting medium ; I 

 have shown how, by making the planets lose energy, their move- 

 ments are accelerated ; on the contrary the action of the tides, 

 by increasing the energy of the moon, retards its movements ; 

 the month lengthens therefore as well as the day. Now if this 

 cause acts alone, what is the final state towards which the system 

 will tend ? Obviously this action would only stop when the 

 tides have ceased — that is to say, when the rotation of the earth 

 would have the same duration. 



This is not all : in the final state the orbit of the moon must 

 have become circular. If it were otherwise, the variations of 

 the distance of the moon to the earth would suffice to produce 

 tides. As the movement of rotation would not have changed, 

 it would be easy to calculate what angular velocity would be 

 common to the earth and to the moon. One finds that, at the 

 limit, the month, like the day, would last about sixty-five of our 

 actual days. 



Such would be the final state if there were no resisting 

 medium, and if the earth and the moon existed alone. 



But the sun also produces tides, the attraction of the 

 planets likewise produces them on the sun. The solar system 

 therefore would tend to a condition in which the sun, all the 

 planets and their satellites, would move with the same velocity 

 round the same axis, as if they were parts of one solid invari- 

 able body. The final angular velocity would, on the other hand, 

 differ little from the velocity of revolution of Jupiter. This 

 would be the final state of the solar system if there were not a 

 resisting medium ; but the action of this medium, if it exists, 

 would not allow such a condition to be assumed, and would end 

 by precipitating all the planets into the sun. 



It must not be thought that a solid globe which was not 

 )vered by seas would, by the absence of tides, find itself free 

 rom actions analogous to those just mentioned, even by ad- 

 mitting that the solidification had reached the centre of the 

 globe. This body, which we suppose solid, would not on that 

 account be an invariable one ; such bodies only exist in text- 

 books on rational "mechanics." It would be elastic and be 

 subject, by the attraction of neighbouring celestial bodies, to 



deformations analogous to tides and of the same order of 

 magnitude. *-««» 



If the elasticity were perfect, these deformations would occur 

 without loss of work, and without the production of heat. But 

 perfectly elastic bodies do not exist. There would be in con- 

 sequence development of heat, which would take place at the 

 expense of the energy of rotation and translation of the bodies, 

 and which will produce absolutely the same effects as the heat 

 engendered by the friction of the tides. '^S IC;:^ 



This is not all : the earth is magnetic, and very probably the 

 other planets and the sun are the same. The following well- 

 known experiment is one which we owe to Foucault : a copper 

 disc rotating in the presence of an electromagnet suffers a 

 great resistance, and becomes heated when the electromagnet 

 is brought into action. A moving conductor in a magnetic field 

 is traversed by induction currents which heat it ; the produced 

 heat can only be derived from the vis viva of the conductor. 

 We can therefore foresee that the electrodynamic actions of the 

 electromagnet on the currents of induction must oppose the 

 movement of the conductor. In this way Foucault's experiment 

 is explained. The celestial bodies must undergo an analogous 

 resistance because they are magnetic and conductors. 



The same phenomenon, though much weakened by the dis- 

 tance, will therefore be produced ; but the effects, being pro- 

 duced always in the same direction, will end by accumulating ; 

 they add themselves, besides, to those of the tides, and tend to 

 bring the system to the same final state. 



Thus the celestial bodies do not escape Carnot's law, accord- 

 to which the world tends to a state of final repose. They 

 would not escape it, even if they were separated by an absolute 

 vacuum. Their energy is dissipated ; and although this dissi- 

 pation only takes place extremely slowly, it is sufficiently rapid 

 that one need not consider terms neglected in the actual 

 demonstrations of the stability of the solar system. 



ON THE USE OF METHYLENE BLUE AS A 

 MEANS OF INVESTIGATING RESPIRA- 

 TION IN PLANTS. 

 TT has long been known that methylene blue is capable of 

 -*■ being decolorised by reducing agents, and the object of the 

 present communication is to point out its use as a means of 

 demonstrating in a striking manner the reducing power possessed 

 either by living protoplasm or at any rate by substances intimately 

 associated with the exercise of its vitality. Its employment is 

 not new to animal physiologists, but botanists appear not to have 

 recognised the possibilities latent in the method, perhaps 

 because some ten years ago Pfeffer (" Oxydationsvorgiinge in 

 Lebenden zellen") stated that although fermenting yeast would 

 decolorise the blue solution, green plants would not do so. 

 Doubtless this was true under the conditions of Pfeffer's 

 experiments, but nevertheless many green plants are, as a matter 

 of fact, found to give admirable results. 



If germinating seedlings of barley or peas be placed in test 

 tubes filled with a 00005 P^'' cent, solution of methylene blue, 

 which has been boiled in order to expel air, it will be found that 

 in the course of a few hours the liquid around them will have 

 lost its colour. The most striking way of performing the 

 experiment is to suspend the peas in the solution, then a 

 decolorised zone is formed between the upper and lower parts 

 of the liquid, each of which still retain its blue colour. 

 Gradually the clear zone extends until the entire mass of the 

 liquid, except just at the surface where it is in contact with the 

 air, becomes decolorised. At first the radicles of the seedlings 

 are strongly stained ; they finally again become white. 



If some of the decolorised liquid be drawn off by means of 

 a pipette, and shaken up with air, the blue tint speedily returns. 

 If some of the seedlings be removed from the now colourless 

 liquid, and be rinsed in boiled water and then exposed to the 

 air, they soon become blue, and the stain gradually extends into 

 the internal tissues as these become gradually aerated. The 

 " development " of the blue can readily be seen in sections, 

 quickly made, under the microscope. 



Cress seedlings are far more active than either barley or peas, 

 just as would have been expected from the relations which they 

 exhibit towards oxygen. 



But perhaps the most remarkable results are thosej ob- 

 tained from a plant like Chara. This alga is suspected 

 to possess peculiar properties in regard to its connection with 



NO. 1495, VOL. 58] 



