388 



NA TURE 



[Mar. 19, 1874 



cord the exact temperature at any hour it may be deemed 

 desirable, and by its means, and with experiments carried 

 over some period of time, we may be able to determine 

 with a degree of accuracy hitherto only approximately 

 arrived at, which are the coldest or warmest periods of 

 the days or nights. 



ON SOME RECENT ASTRONOMICAL SPE- 

 CULATIONS IN THEIR RELATION TO 

 GEOLOGY* 



I HAVE called my subject speculations, because in the 

 present state of the inquiry there are so many ques- 

 tions that can be looked upon in no other light. At the 

 same time it appears to me very desirable that certain 

 facts should be examined from this new point of view, if 

 only to lead to researches which otherwise would not 

 have claimed attention. What I then propose is to con- 

 sider the bearing on certain geological questions of the 

 new views of Mr. Lockyer respecting the constitution of 

 matter, as indicated by a comparison of the spectra of the 

 various classes of stars, and the probable effects of a 

 change in the constitution of our sun.f 



Sir W. Thomson has contended that the stin cannot 

 have continued to give out heat and light for so long a 

 period as has been assumed by many geologists, and has 

 concluded that it was " on the whole most probable that 

 it has not illuminated the earth for 100 millions of years, 

 and almost certain that it has not done so for 500 mil- 

 lions."+ Prof. Huxley made this question the subject of his 

 address to the Geological Soci'ety in 1869, but the argu- 

 ment on both sides was on the supposition that the con- 

 stitution of matter is such that from the earliest epoch 

 the heat and light given off had been derived mainly, if 

 not entirely, from the simple cooling of a heated body. If, 

 however, Mr. Lockyer's views be true, the sun at the 

 earliest period must have consisted of matter in a more 

 dissociated condition than at present, and, as he points 

 out, in combining so as to give rise to other so-called 

 elementary substances, probably a large extra amount of 

 heat and light would be set free. The result of this 

 appears to me to be that when the general temperature 

 was that at which such a dissociation occurs, the sun's 

 energy would continue nearly the same for a period which 

 in the present state of our knowledge cannot be deter- 

 mined, but which would probably be of vast duration ; 

 and not only so, but the cooling would be more uniform 

 from the first, and not subject to so great a variation as 

 would occur in the case of an intensely-heated body cool- 

 ing without any physical change in its constituents. If 

 this be so, the length of time during which our globe may 

 have been receiving such an amount of heat and hght as 

 would be compatible with the existence of animals and 

 plants may well have been as great as that demanded by 

 any of the supporters of evolutionary theories. 



Though there would be such an approximate uniformity 

 for a vast period, yet still at the earliest epoch, the physical 

 state of the sun would not have been the same as now, 

 and it becomes important to consider what effect this may 

 have produced on life on the globe. According to Mr. 

 Lockyer's views the sun at an caily period liad much the 

 same physical constitution as the stars of the type of 

 Sirius, giving off light of a whiter or bluer character, />. 

 the rays at the blue end of the spectrum were relatively 

 stronger than at present, whilst in future ages they would 

 become more feeble, and the sun pass into the condition 

 of stars of the red type. What then would be the effect 

 of the greater intensity of the rays at the blue end of 



* An abstract of a paper read before the Sheffield Literary and Philoso- 

 phical Society, Feb 3, 1874, by H. C. Sorby, F.R.S, 

 t Comptes Rendiis, Dec. 8, 1873. 

 j Brit, Ass.JReport, 1861, p. 28. 



the spectrum on animals and plants at early geological 

 epochs } This question clearly indicates the importance 

 of future experimental inquiries, directed to this particular 

 subject, but at the same time it may be well to consider 

 the bearing of what is already known. In the present 

 state of our knowledge no facts seem more likely to help 

 towards a conclusion than those connected with the dis- 

 tribution in plants of the more important of the coloured 

 substances which absorb different rays of light. I have 

 found that there is an intimate relation between their 

 optical and chemical characters, and that these are also 

 related to the development of the individual plants, 

 and to the structural development of mature plants 

 of different classes. Taken as a whole, in advancing 

 from a more rudimentary condition, there is in each 

 case a farther and farther departure from such co- 

 louring-matters as can be formed artificially, and a 

 relatively greater and greater production of those which 

 are more and more easily decomposed by light, when 

 not protected by the constructive energy of the living 

 plants. This destructive action is due relatively more to 

 the rays at the blue end of the spectrum, whilst, at all 

 events in the case of chlorophyll, the production depends 

 more upon the yellow rays. Hence, by relatively in- 

 creasing the intensity of the blue rays the destructive 

 force would be relatively increased, and the constructive 

 force relatively diminished. We may, perhaps, therefore 

 conclude that bluer light would be relatively more favour- 

 able to the higher classes of pLmts when in the early 

 stage of their growth, and to the lower than to the higher 

 classes when in the mature condition requisite to insure 

 permanent reproduction. The former conclusion is borne 

 out by Mr. Robert Hunt's experiments, which showed that 

 whilst the rays at the blue end of the spectrum 

 quicken the germination of the higher classes of plants, 

 it is the rays at the extreme red end which facilitate 

 their flowering and the perfecting of the reproductive 

 organs.* The effect of differently coloured light on the 

 growth of the cryptogamia has not, I believe, been exa- 

 mined ; but, if the principles involved in the above 

 arguments be correct, they would lead us to conclude 

 that at an early epoch in the history of our globe the bluer 

 light of the sun would be relatively more favourable to 

 the growth of larger cryptogams than to that of phano- 

 gams. The arguments I have used do, however, involve 

 so many new and imperfectly -tried general principles, that 

 it would be very premature to say that the characteristic 

 peculiarities of the vegetation of the earlier geological 

 periods depended on this cause, and all that I contend is 

 that the question deserves to be examined from this new 

 point of view, since it may at all events assist in arriving 

 at a true explanation. 



THE "CHALLENGER" EXPEDITION \ 



II. 



Fernando Noronha 



npiIlS group of islands was visited by the CluilUngcr 

 -'- on September I and 2, 1S73. They consist of a 

 principal island, about four miles long, and three-and-a- 

 half broad, stretching about N.E. and S.W., and several 

 smaller ones at the eastern extremity, known as Platform 

 Island, Booby Island, St. Michaers Mount, Egg Island, 

 and Rat Island. They are situated in the Atlantic, in 

 lat. 30° 50'', about 200 miles fiom the nearest point of the 

 South American coast, their entire length being about 

 seven miles. The principal island is generally of a 

 volcanic character, and hilly, the highest hill being about 

 600 feet. On its northern coast rises to a height of 1,000 

 feet what is known as the Peak. It is a peculiar-looking 



^ Brit. Ass. Report, 1843, p. 35. 

 t These Notes are founded on letlcrs sent Home by Mr. H. N. Mosely. 



