NATURE 



\_Nov. 7, 1878 



velocity, i.e., a velocity to which apparently no limits can be 

 set. It is true that the molecules which in the accidents of col- 

 lision among themselves acquire these enormous velocities, have 

 been mathematically proved to be relatively few in number, the 

 greater nimiber of the molecules possessing velocities approachin;^ 

 the mean value. But it would seem to follow necessarily that 

 molecules situated in the top stratum of any atmosphere, and 

 i^ich acquire these enormous (indeterminable) velocities, can 

 sometimes overcome gravity, and be projected into space, so as 

 not to return ; as it is a known fact that only a Jinite velocity is 

 required to effect this result. I have therefore to suggest that 

 by this cause the moon's atmosphere has gradually disappeared. 

 It is probable, no doubt, that it would take a vast period of 

 time to have brought about this result, but we have an almost un- 

 limited time at disposal. It might possibly be asked. How is it that 

 the earth's atmosphere has not shared the same fate? In answer to 

 this I would reply, first, that the value of gi-avity on the earth is 

 known to be very much greater than on the moon, and second, that 

 possibly (for aught we can tell) part of the earth's atmosphere 

 may have thus disappeared ; or the earth's atmosphere may be 

 less dense at present than at one time, for anything we can say 

 to the contrary. It would seem a curious fact to note in con- 

 nection with this that there would be apparently grounds for 

 inferring that the constitution or composition of the earth's (or 

 any other planet's) atmosphere might have changed from the 

 above cause, as evidently the lighter gaseous constituents, whose 

 molecules acquire in the accidents of collision the highest veloci- 

 ties, would be first dissipated into space in the above manner. 

 Thus, for example, any trace of that very prevalent constituent 

 of the universe, hydrogen, that might have at one time existed 

 in the earth's atmosphere, would have tended to become relatively 

 rapidly eliminated, as the molecules of hydrogen are known to 

 possess a normal velocity about four times as great as that of the 

 constituent molecules of the earth's atmosphere.^ It might be 

 said that changes so great as those above indicated are scarcely 

 realisable, but then it should be kept in view that w^e have an 

 almost limitless range of time to draw on, and it is generally 

 admitted to be very important to take the effect of time into due 

 consideration, as, for example, is done in the case of geology, 

 where mountain ranges are recognised by incontrovertible physical 

 proof to have been carved out by the slow disintegrating action 

 of rain and atmospheric influences prevailing through countless 

 centuries. The gradual disappearance of an atmosphere (earth's 

 or moon's) under the above cause might possibly be compared in 

 slowness of operation to the other cosmical changes that the 

 solar system is known to be undergoing, such as the gradual 

 approach of the earth to the sun (and of the moon to the earth) 

 through the friction of the material media in space, the accom- 

 plished stoppage of the moon's axial rotation by tidal action on 

 its mass, and the gradual diminution of the earth's rotative 

 velocity from the same cause. These slow changes, imper- 

 ceptible in the range of human experience, become important in 

 large time epochs, and it becomes desirable in the interests of 

 truth, in tracing back events, to give due weight to these time 

 epochs. In suggesting the above explanation, I have endeavoured 

 to confine myself strictly within the limits of mathematically 

 proved facts as a basis to draw deductions upon, and I should 

 be glad to accept any criticisms that might be offered, either with 

 the view to point out a difficulty or confirm the truth. 

 LondoUj^Qiftober S. Tolver Preston 



Remarkable Local Colour-variation in Lizards 



The following extract from a letter received some months 

 since from Baron de Basterot, of Rome (a Fellow of the Geo- 

 logical Society of London), records an interesting case of local 

 colour-variation, about which some of your correspondents may 

 be able to give us further information : — 



"Capri is a mass of the usual yellowish- white Apennine 

 limestone, forming precipitous cliffs nearly all round the island. 



' The realisation of a possible diversity at a former epoch in the constitu- 

 tion and density of the earth's atmosphere raises rather a curious question in 

 connection with the known diversity of the plants and animals that formerly 

 inhabited the globe, as compared with those at present existing. It might be 

 observed that admitting the possibility of the former existence of an atmo- 

 spihere on the moon, it would seem to follow that an interchange of molecules 

 between the two atmospheres (those of the earth and moon; must have taken 

 Iilace at one time to a certain extent under the above cause, though the con- 

 siderably less value of gravity on the moon compared with the case of the 

 earth would facilitate the passage of molecules away from the moon and 

 lender correspondingly difficult the passage in the reverse direction. 



At its southern extremity are three high and nearly inaccessible 

 rocks called I Faraglioni, one of which, pierced by a natural 

 arch, has been frequently depicted by artists. Two of these 

 rocks are completely detached from the mainland, and, I need 

 hardly add, uninhabited. 



"On the island, and on the first of the Faraglioni rocks which 

 is connected with it, the lizards are of the usual species so 

 common in Italy — coloured grey, mixed with more or less green. 

 On the two outward FaragUoni rocks, which are completely 

 separated from the shore, their colour is totally different. The 

 back is of a blue so dark as to appear nearly black ; the sides 

 of a brilliant blue, like lapis-lazuli ; the belly light whitish-blue, 

 Avith a very slight tinge of green. 



"An English gentleman whom I met in Capri had several of 

 these lizards alive, which had become quite tame in the course 

 of a couple of months. I believe he intends bringing them to 

 England. He is of opinion that they differ in colour only from 

 the lizards of the island, and that, though very different in 

 appearance, they are the same species. 



" Whether this be so, or whether they are specifically differ- 

 ent, their presence on these isolated rocks and their total 

 absence on the island is equally remarkable." 



Alfred R. Wallace 



Termites kept in Captivity by Ants 



^ When entomologising in Portugal in 1877, in the neighbour- 

 hood of Cintra, I found the nest of Formica nigra under a stone. 

 On my turning it over there was, as usual, great consternation 

 in the community, and I discovered that it was evidently caused 

 by the fear lest a colony of Termes hicifugus, which the Formicas 

 had enslaved, should escape. The Nigras instantly began seizing 

 the Termites, driving them underground by the nearest orifices, in 

 the meantime wrenching and pulling off their a\ ings in the most 

 unceremonious manner. I observed a large number 'of wings 

 lying in heaps here and there in the nest as if this treatment had 

 been practised before. In the nest there was also a great number 

 of Termite larvje. The great object of the owners of the " loca- 

 tion" seemed to be to get these larvas underground as speedily 

 as possible. The ants fell on them with great impetuosity, 

 seizing them anyhow and anywhere, dragging them against the 

 most strenuotis opposition (their behaviour strikingly contrasting 

 with the meekness of their winged fellows) into the nearest 

 apertures of the underground home. Very often this oppo.«ition 

 resulted in a long and stern fight, in which the larvje were often 

 badly wounded, being deprived sometimes of their antenna?, 

 sometimes of half their jaws, and not seldom killed outrij^ht. 

 Occasionally, however, the larv?e were victorious, beating off the 

 Formicas, in which case they (the larvce) did not make off, but 

 remained perambulating the nest. I saw one larva drawn at the 

 end of a long fight by its antenna, while it strenuously held on 

 to a small ball of earth which had proved a vain anchorage for 

 its feet, for larva and clod together were dragged across the top 

 of the nest (made by the impression of the stone) five or six 

 inches, up the side, i| inch, and away among the grass, where, 

 losing the ball of earth, it seized a stalk so firmly that its abductor 

 could not drag it farther, whereupon, after reconnoitring the 

 ground for a little distance the latter disappeared, but returned 

 shortly with a companion, with whose aid the larva was detached. 

 This done, the helper returned home while the abductor pro- 

 ceeded with his prisoner till lost to view in the grass, some 

 twelve or fourteen inches from the spot whence it originall}- 

 started. 



In the same neighbourhood I watched for some time a nest of 

 Formica ligniperda. An injured female was placed in the nest, 

 but no assistance was rendered, while it crawled along towards 

 the nearest orifice leading underground. At the spot where 

 this individual was injured some of the fluid of its body which 

 had oozed out ■^^■as eagerly lapped up by the others ; some even 

 applied their mouths to the wounds on the body. During the 

 operation of lapping the maxillse were kept perfectly still, and 

 the antennse close to the side of the head " feel -feeling " the 

 ground with the tips, as if to discover the spot where the liquid 

 was to be found. Every now and then, however, they were 

 extended at right angles to the body, as if to obtain a more 

 general survey of things, and then immediately returned to their 

 previous position. On several of those which were busy lapping 

 I poured some spirits of wine. They instantly became stupefied, 

 and for a time motionless. When in this condition they were 



