74, 



* KNOWLEDGE ♦ 



[Nov. 25, 1881. 



" Tyro's" otlicr quorj" (lottor 9, p. 30) is one often made, thougli 

 rnont text-books siilliciiiitly explniii tlio ilifliciilty. The only kiml 

 of rovulution which some renUors of astrononiicnl works st'em 

 capable of iimlerslanding is such as wo boo where a ball at the end 

 of n riffid timI is swnyed by the rod round a centre. Tho real revo- 

 lution of the earth more nearly resembles tho motion of a spinning 

 top when thrown (on a curved path) through (he air, tho axis 

 moving oil the time parallel to itself, or retaining an unchanged 

 direction while ehanping constantly in place. 



In my remarks on letter 13, p. 37, tho words ten millions, last 

 lino but two of second parafrraph, should bo ten billions. There 

 aro in nil more than twenty millions of millions of possible positions 

 in tho " fifteen puzzle," though some, overlooking the circuuiiitance 

 that every change in tho position of the blank square changes the 

 pnzzle, suppose there are only about li millions of millions. 



As regards query 3, p. 30, on the flight of birds, it is quite certain, 

 as others, I sec, have pointed out, that tho air in tho passages of 

 tho bones cinnot help the bird by adding toils buoyancy. If an 

 absolute vacuum could bo produced in these passages, which (if the 

 passages remained unchanged in volume) would give the maximum 

 degree of buoyancy, the only lifting power which would result would 

 be simply e(|uivalent to the weight of so much air at tho actual 

 lenipei-iture of the air in which the bird is flying at tho moment, as 

 would till the passages in the bones. Air equal in volume to the 

 bird itself would not h.ivo nioro than a lOOtli jiart of his weight; 

 how much less, then, would the counterpoising of his weight by a 

 raising power corresponding to tho weight of the tiny quantity of 

 air which would till tho passages, be of any appreciable avail iu 

 helping him to tly ? 



I will describe and sketch in an early number a very simple 

 instrument for telling time from a shadow (as in the case of the 

 sun-<lial), without any appreciable error arising from the shadow 

 not being sharp. Kich.\kd A. Peoctoe. 



THE MISSIXG LINK. 



[33] — I am glad to see a con-espondent ("An Ignoramus") has 

 asked for an explanation regarding the "Missing Link" of Dar- 

 winism and Evolution. Briefly stated, here is the problem. If, as 

 evolution postulates, the various forms of animal life have "sprung 

 from one, or, at most, a few, primitive forms, then we must con- 

 ceive of living nature as a tree of which all the parts are connected 

 together from root to topmost twig. Now, if man exists, as he 

 unquestionably does, at the top of the highest twig, it is evident he 

 must bo connected, by some forms more or less like himself, with 

 lower quadrupeds, and through these latter, with still loner 

 animals, and so on. Where, then, in tho case of man, are the 

 animal links that lead from the human to the pre-human, and 

 from the lu'ohuman to the purely animal ? When evolu- 

 tion was first promulgated, everybody asked " Where are 

 tho missing links ? " That common ignorance, which too often 

 passes for common sense or for science, at once inquired where was 

 tho link that connected man with the monkey ? This question is 

 founded on gross ignorance of what evolution requires. Xo evolu- 

 tionist assumes that man is descended from any existing ape, or 

 from an'j e^Hiict ape eilhcr. Sir. Darwin, in his "Descent of Man," 

 is very careful to point this out. What evolution does say is, that 

 probably man and apes originated far back in some common root- 

 stock, whence the human branch proceeded, diverging for ever, from 

 the ape branch, on its own way of development. If we take the 

 four highest apes — gorilla, chimpanzee, orang, and gibbon — we find 

 no one of tho four to approach man as a whole more nearly 

 than any other of the four. If an approach to the human frame 

 were t» be made from tho apo-side, wo should require a bit from 

 each and all of the four to make up such a representation of the 

 human type. The orang's brain is, for instance, more like man's 

 than the gorilla's, but tho latter approaches man's more nearly in 

 some other points. It is the same with the gibbon and the chim- 

 panzee. The " old ladies of both sexes," who used to assume that 

 the gorilla as the " missing link " was a failure, did not know that 

 tho evolutionist thoroughly agreed with them. Where the " links" 

 that connect man to his lower neighbours are to be found, is a 

 difficult question to answer. Possibly we must go first to lower 

 human life, and find an ai)i)roach to animal characters in tho skulls 

 of savages and primitive men (e.g.. Neanderthal skull) ; but the 

 geological record is imi>erfoct. There are long gajis in tho series 

 which can never bo filled. All living foi-ms have not been preserved 

 in the fossil series. With human remains, the chances of preservation 

 aro few and far between. Even primitive man buries or burns his 

 dead; and thus tho record of man's past history may ever remain 

 obscure. liut all the evidence points indubitably to man's origin 

 from lower life. His development shows this idea to be true ; tho 

 presence of rudimentarj' organs (such as ear-muscles, which are of 

 no uso to him) tells tho same talo ; and anthropology, in its re- 



searches into savage life and customs, verifies evolution. I hope 

 "Ignoramus" will feel satisfied with tho above answer. He 

 should road Darwin's "Descent of Man" and Mr. Tyler's "An- 

 thropologj-," and an article on " Missing Links," in a recent 

 volume of the Ociifd-man'n 3/(i^a:iiie, will also help him in his en- 

 deavour to understand what evolution demands and implies. 



Anubew Wilson. 



TUE SUN'S UEAT. 



[31] — I mnst confess I was somewhat surprised to read " Anti- 

 Guobre's " letter in your first issue, considering tho preceding 

 remarks about " paradoxers ; " but since he asks for information, 

 I shall be glad to give it him. 



In the first jjlace, the air is not capable of being directly warmed 

 by the rays of tho sun, but it is warmed by contact with the 

 heated earth ; consequently the air is much warmer in the valleys 

 than on the tops of the mountains, .\gain, in tho valleys tho air is 

 not so subject to disturbance by winds, Ac, as it is at a higher 

 elevation ; so when we ascend a mountain or rise in a balloon, we 

 recede both from the body of the earth and from tho heat thereof, 

 for air is a ver)- bad conductor of heat ; but though the air is colder, 

 the sun's rays aro not. If " Anti-Guebre" had ever ascended a 

 snow-capped mountain, ho would know that the rays of the sun are 

 insupportably hot there : for two reasons ; first, the traveller is 

 nearer tho sun, and unprotected by clouds and aqueous vajwnr ; 

 secondly, he is exposed to the reflection from the snow. The snow 

 protects the mountain itself from being much warmed, and is oidy 

 very slowly melted, as it reflects tho greater part both of the heat 

 and light. The deposition during the night makes up for the loss 

 experienced during tho day. Alpine climbers asually complain that 

 tlioir lower limbs are nearly frozen by the snow, while their heads 

 and shoulders are almost roasted by the snn. 



Aqueous vapour jdays a very important part in the warming of 

 air, for it is the vapour rather than the air itself that receives tho 

 heat. Dry air cannot be warmed so easily as damp air. This is the 

 reason why the air feels warm in drv% ftosty weather, as it cannot 

 conduct away the heat from the body ; whereas, damp air feels 

 colli, since tho aqueous vapour does conduct aw.iy the animal 

 warmth of our bodies. (Of course, I am not considering the subject 

 of evaporation.) At high elevations the air is colder and dryer 

 than at the surface of the earth. 



With regard to the icy nature of cirrus clouds, there is nothing 

 absurd iu the supposition. 



Anyone who watches the sky in summer will see clouds disappear 

 and reform, often with great rapidity. Tliis is due to the varying 

 temperatuie of the air, or rather of the air currents, which either 

 condense or volatilise the aqueous vapour in the air, according to 

 their temperature. We know that certain clouds do consist of icy 

 particles when we see a halo round the moon making a particular 

 angle with the observer's eye. If "Anti-Guebre" thinks an ice- 

 cloud ought to be instantaneously melted by the heat of tho sun, he 

 is in error, as, putting on one side tho diathermancy of ice, and 

 granting that the action of the sun would bo to melt it, the 

 evaporation at that altitude would be so rapid as to freeze again 

 the water formed, consequently, the volatilisation of the cloud 

 would take some time. 



" Anti-Gnebre's " " profit and loss " ideas of the solar system aro 



too deep for me. It is true that we only receive 



' 2,O70,650,tXK) 



of tho sun's light and heat ; but what right has ho to say that tho 

 rest is wasted ? lie must fii-st find out what becomes of it, and 

 prove that it does no work. He might, with equal truth, say his 

 own time is wasted when in bed, because he is not conscious of 

 what takes place when he is asleep. — 1 am, ic, Sm. 



THE SUN'S HEAT (Abstract). 



[35]—" Anti-Guebre" says that when he approaches the fire ho 

 feels warmer, but that, on tho contran,-. an approach to the sun 

 produces a cooling effect, hence tho sun is cold. In the case of 

 the fire wo make a very groat difference in thobsolute [it should 

 bo relative] distance between us and it, by a very small movement 

 on our part ; whilst in the case of the sun, any difference in tho 

 absolute [relative] distance between us and that orb which we are 

 able to make is immeasurably small compared with tho absolute 

 distance ; and though it may be said there noiild be an augmenta- 

 tion, though small, there are other causes at work which more than 

 neutralise this augmentation. 



It has, I think, been fully proved that the air itself is transparent 

 for heat, and that the air is narmcd by contact with the earth ; the 

 higher, therefore, we rise above the sea-level, the colder does tho 

 air become, and this effect is ample to overcome any slight increase 

 in tho heating power, owing to a decrease in tho direct distance of 



