476 



IfATURE 



[Oct. lo, 1872 



by the name of VoUananuia Binncyi to be the cones of 

 Calaniites. On the other hand, whilst I do not deny that 

 such may possibly be their nature, I contend that we 

 have neither proof nor even probable evidence sustaining 

 this idea. Dr. Dawson says that Asterophyllites and 

 Annularia arc very distinct plants. Mr. Carruthcrs 

 affirms that they are not. ]\I. Grand-Eury and myself 

 contend that Asterophyllites is wholly distinct, both 

 in type and organisation, from Calamites. Mr. 

 Carruthers believes that Asterophyllites and Annu- 

 laria .ire alike the foliage of Calamites. It would 

 be easy to multiply illustrations proving the exist- 

 ence of these opposite conclusions on important 

 points amongst those observers who have enjoyed the 

 best opportunities of forming reasonable opinions on 

 such subjects. It is sufficiently obvious that some of us 

 must be in error on these questions ; possibly each of us 

 is so in a greater or less degree ; but when we regard the 

 scientific status of the observers to whom I have referred, 

 leaving myself out of the question, I ask, are they men 

 whom we can accuse lightly of carelessness or ignorance ? 

 Must we not rather infer that each man has observed 

 special facts leading him to his own conclusions, and that 

 what we want is a careful comparison of such facts with 

 those which have led our fellow-labourers in an opposite 

 direction to ourselves? Whatever may be the explanation 

 of these discrepant opinions, surely our mutual duties are 

 clear. If any of us thinks that his fellow-labourer has 

 made mistakes (and who lias not) let him say so openly, 

 and not suggest the idea by indulging in deprecatory in- 

 sinuations. Let his opposing argumctitHm be ad 7 cm, and 

 not nd hoDiiiion. Further, let it be ad rcDi and not ad 

 alteram rem. Let it not rest upon mere analogies, which 

 may or may not be sound. Let us not reject a conclusion 

 before we know all the facts fiom which it is drawn, 

 merely because we think we have reason to deem it an 

 impossible one. We have all lived to see many such 

 conclusions take their places as undoubted truths. 



One source of danger on these 'points, in the case of 

 fossil botany, arises from the circumstance that though 

 the ancient types of vegetation bear definite relations to 

 the living ones, very remarkable differences present them- 

 selves in the combinations of the vegetative and repro- 

 ductive organs in the two cases. Who, for instance, could 

 have anticipated, from his knowledge of living plants, 

 such an union of the usu.al vegetative organs of a cycad with 

 an altogether anomalous reproductive system as we see in 

 ]\'i/liaii!soi!ia L;/i;as. Many such examples will occur lo 

 those familiar with the subject. Hence, whilst a knowledge 

 of living plants is absolutely indispensable to the student 

 of fossil botany, — he cannot have too much of it — we 

 must not allow our knowledge of recent combinations of 

 vegetative and reproductive structures unduly to bias our 

 judgment as to what may occur amongst fossil plants. 

 Whilst we fully recognise the persistence of types, we 

 must equally recognise the wonderful modifications which 

 they h.ave undergone in prim:cval times. 



The conclusions to which these views lead me are very 

 simple ones. The complex problems of palreophytology 

 require harmonious and trustful co-operation amongst 

 observers if truth is to be discovered. Let us supply tliis 

 in the spirit of cordial fellow-labourers, and not as rivals 

 in jnirsuit of a fleeting reputation which cannot be shared 

 with others. We shall never raise ourselves by pulling 

 others down. I will not quote the special expressions tiiat 

 are present to my mind whilst penning these lines : but it 

 would be easy to do so, and to show that no possible 

 benefits can accrue to science from their use. We can 

 easily correct our mutual errors, we cannot so easily 

 sooth wounded feelings, or restore shaken confidences. 

 AVe aim at being the high priests of nature ; let us try to 

 banish all disturbing personal and selfish influences from 

 the temple. 



These words of warning may appear superfluous, be- 



cause they embody mere truisms, equally applicable to 

 every branch of human inquiry, or impertinent, seeing 

 that in the fervour of earnest work, I may have erred in the 

 same way as my neighbours. The fact is, that, like others 

 of my earlier fellow-workers, I am rapidly approaching the 

 autumn of life, and peace and hannony now appear more 

 precious to me than they did in bygone years, when 

 youthful ambition was alike active and inconsiderate. 

 Happily ours are not pursuits which require us to cry ?■<? 

 viclis ! Just in proportion as we meet our opponents in a 

 loving and harmonious spirit, without abandoning, in any 

 degree, our earnest contention for what we believe to be 

 truth, shall we, in our declining years, review our past 

 labours with satisfaction and not with sorrow. — Sic csto. 

 W. C. Williamson 



DISTRIBUTION OF HEAT IN THE 

 SPECTRUM 

 pROF. J. W. DRAPER has commimic.ated to SiUimaii's 

 -'■ Journal of Scioice and Art for .September a very 

 important article under the above heading. After detail- 

 ing a series of experiments on the distribution of the heat 

 of the whole visible spectrum, of the more refrangible 

 and of the less refrangible region, by rock-salt, flint-glass, 

 bisulphide of carbon, and quartz, he thus sums up the 

 results : — 



" The important fact clearly brought into view by these 

 experiments is, that if the visible spectrum be divided 

 into two equal portions, the ray h.aving a wave-length of 

 576S being considered as the optical centre of such a 

 spectrum, these portions will present heating powers so 

 nearly equal that we may impute the differences to errors 

 of experimentation. Assuming this as true, it necessarily 

 follows that in the spectrum any two series of undula- 

 tions will ha\e the same heating power, no matter what 

 their wave-lengths may be. 



" But this conclusion leads unavoidably to a most im- 

 portant modification of the views now universally held as 

 regards the constitution of the spectrum. When a ray 

 falls on an extinguishing surface heat is produced, but 

 th.at heat did not pre-exist in the ray. It arose from the 

 stoppage of ether waves, and is a pure instance of the 

 conversion of motion into heat — an illustration of the 

 modern doctrines of the conservation and transmutation 

 of force. 



" From this point of view the conception that there exist 

 in an incident ray various principles disappears alto- 

 gether. We h.ivc to consider an incident ray as con- 

 sisting solely of etherial vibrations, which, when they are 

 checked by an extinguishing substance, lose their t7> 

 viva. The effect that ensues depends on the quality of 

 the substance. The vibrations imparted to it may be 

 manifested by the production of heat, as in the case of 

 lamp-black, or by chemical changes, as in the case of 

 many of the salts of silver. In the jjarallel instance of 

 acoustics clear views have long ago been attained, and 

 are firmly held. No one supposes that sound is one of the 

 ingredients of the atmosphere, and it would not be more 

 incorrect to assert that it is something emitted by the 

 sounding body than it is to affirm that light or heat, or 

 actinism, are emitted by the sun. 



"The progress of actino-chemistry would be greatly 

 accelerated if there could be steadfastly maintained a 

 clear conception of the distinction between the mechanism 

 of a ray and the eflccts to which that ray may give rise. 

 The evolution of heat, the sensation of light, the produc- 

 tion of chemical changes, are merely eft'ects — manifesta- 

 tions of the motions imparted to ponderable atoms — 

 and these in their turn can give rise to converse results, 

 as when we gradually raise the temperature of a sub- 

 stance the oscillating movements of its molecules arc 

 imparted to the ether, and waves of less and less length 

 i are successively engendered." 



