Dec. 25, 1879] 



NATURE 



177 



earth, and going vertically upwards, Mr. Schlemuller finds the 

 height of an atmosphere 



Of pure oxygen 43,360m., or 27 miles 



Of pure nitrogen 49,360m., or 31 miles 



Of watery vapour 76,980m., or 48 miles 



These results are, indeed, fair approximations to the ordinary 

 values. 



At the end of his treatise the author gives some formulae 

 which are destined to serve for the measurement of heights by 

 means of the barometer and thermometer. 



On p. 10 there is a curious statement. Supposing the air or 

 gas to be inclosed in a vertical " narrow tube," the author thinks 

 that the molecules will be able to make vertical movements only, 

 and he introduces, therefore, into his calculations the mean value 



y 

 of the vertical components of their velocity, viz., — . The result 



is that, according to Mr. Schlemuller, the temperature in a narrow 

 vertical tube, open at top and bottom, increases four times faster 

 towards the bottom than in the free atmosphere. What the 

 author considers to be a "narrow rube" he shows on p. 12, 

 where he applies his rule to a pit or well(!). It is not too 

 much to say that a perpetuum mobile might be constructed on 

 that principle. 



Mr. Schlemuller's formula for measuring heights might be 

 perhaps accepted by some who would take the numerical results 

 given by the author as a sufficient proof of his theory. It is, 

 however, impossible that a theory resting on false assumptions 

 should give correct results, and the coincidence of the results 

 given with data derived from other sources is only apparent. 

 First these data themselves are so varying that it is not very 

 difficult to produce a number approaching pretty closely to some 

 of them ; on the other hand, the results calculated from a theory 

 which supposes an atmosphere not exposed to radiation ought 

 not to coincide with data derived from the actual atmosphere, 

 which is far from fulfilling the conditions supposed by the 

 theory. L. Hajnis 



Prague, December 3 



Alternative Interpretation of Sensation 



The curious optical phenomena which form the subject of 

 Mr. Ackroyd's letter (Nature, vol. xxi. p. 10S) have their 

 analogues, as many have probably observed, in other orders of 

 sensation. When travelling by railway, or indeed in any closed 

 vehicle, I have often noticed that, if passing objects be shut out 

 from view, it is possible with a little effort to mentally reverse 

 the direction of the train, so that if sensation only were con- 

 cerned, there would be no doubt as to this reversed motion. 

 Another example of this choice of interpretation is also afforded 

 by the sensations of motion, but in a slightly different way. 

 Standing low down by the water, on a moving steamer or on a 

 bridge over a rapid stream, we can at will either feel that we 

 are moving through the water or that we are stationary while 

 the water is flowing by. The same, or at any rate a very 

 similar, choice is presented when the clouds are scudding over 

 the moon's disk ; we can either see the moon travelling behind 

 unmoving clouds, or the clouds passing rapidly across the moon. 



It would appear from the above facts that we have in certain 

 cases the power of selecting from the experiences which have 

 been associated with a given set of sensations that one which 

 we wish the sensations to convey. It is difficult to see how this 

 can be explained without admitting a certain amount of freedom 

 of will, as the sum of our previous experience, including the 

 sensation itself, is the same, whether we choose to go backwards 

 or forwards, to stand still or to move on. Fred. D. Brown 



Science Schools, South Kensington, December 16 



Curious Incubation 



Indian birds avail themselves largely of natural heat in incu- 

 bating ; as breeding-time generally begins in March, the hot 

 weather is generally well on by the time the eggs are laid, and 

 as the temperature of the air is rever below a minimum of 

 98 - loo" during the day, the eggs are but little sat upon except 

 during the night, and so rest and duty are combined judiciously. 



On one occasion I collected birds' eggs, and, until I could 

 blow them, I used to place them in a drawer of my office table, 

 and there they would lie for two or three days until I had leisure. 

 One day, while writing, I heard strange sounds from this drawer, 



and opening it found a young crow (Corvus splemtens) emerged 

 from its egg. On a second occasion I similarly found a young 

 myna. I tried hard to rear these strange hatchings, but failed. 

 One day I saw a kite's nest in the top of a fan palm, and sent 

 up a native to bring down the contents, which turned out to be 

 eggs. In a spirit of mischief I placed them, without saying 

 anything to any one, under a hen which was sitting upon ducks' 

 eggs, and awaited the result. Two days after, my fowl-man 

 came to me with a long and solemn face, and asked permission 

 to address me. That accorded, he mysteriously whispered, 

 " My lord, a great wonder has occurred in the fowl-house; a 

 marvel has happened ; devils have been hatched in the fowl- 

 house." Then began a tableau of descriptive acting which I 

 cannot reproduce. " Did not I place ducks' eggs under that 

 hen, and, my lord, have not ducks flat feet like this (flattening 

 and extending his hand), and noses like this (compressing his 

 thumb and index-finger); have they not, my lord?" On my 

 solemnly assenting, he proceeded : "But these devils, my lord, 

 have feet like this (clawing all his fingers), and noses like this 

 (hooking his thumb and index together at his own nose) ? Oh ! 

 my lord, what shall I do ? " " Well, let me see these devils," 

 I replied, sympathi>ingly ; and we walked off to the fowl-house 

 and found the hen sitting dazed beside her basket, in which were 

 five recently-hatched kites. The finale was tragical, for the 

 poor hen abandoned both her eggs and the kites, and the latter 

 would have died had I not had them replaced in their nest. As 

 it was, the ducks' eggs were abandoned. 



R. F. Hutchinson 



THE GEO LOG Y OF THE HENR Y MO UNTATNS > 



THE Henry Mountains are a group of five peaks, 

 ranging in height from 7,000 to 11,000 feet above 

 the sea, which rise out of the table-land, now so well 

 known to all students of physical geography, to which the 

 American geologists have given the name of the Colorado 

 Plateau. 



They are situated in Southern Utah, and are crossed 

 by the meridian of 1 io° 45' and the thirty-eighth parallel. 



They stand close upon the northern bank of the Colo- 

 rado, which flows past their base in a canon 1,500 feet 

 in depth. 



Mr. Gilbert's account of the geology of these mountains 

 is specially interesting to the student of physical geology, 

 on account of the explanation it contains of the machi- 

 nery by which their uplift was brought about. His views 

 have certainly the merit of novelty, and at the same time 

 the evidence in their favour, if not quite conclusive, 

 carries with it considerable weight. 



All previous speculation on the subject of mountain- 

 building may be grouped under two heads. Nearly all 

 mountain ranges have a central axis or core of crystalline 

 rock. By the older geologists this crystalline mass was 

 looked upon as intrusive, and it was believed that the 

 violent injection of a huge body of molten matter had 

 lifted up the stratified rocks through which it forced its 

 way, and shouldered them off on either side, giving them 

 a dip coinciding in direction and approximately in amount 

 with the slopes of the chain. A section across a moun- 

 tain chain would show, according to this view, an anti- 

 clinal arrangement of the bedded rocks with a body of 

 intrusive rock in the centre, and it was the intrusion of 

 this central mass that was believed to have caused the 

 upheaval. The force, then, which according to this view, 

 raised mountains to their present elevation, was of the 

 nature of a thrust acting vertically upwards. 



Never, perhaps, did any theory collapse more com- 

 pletely than this when it came to be subjected to the test 

 of examination in the field. As mountain chains were 

 one by one investigated by geologists, the anticlinal 

 arrangement of their rocks which this theory required 

 was found to be more and more conspicuous by its 

 absence. Marked peculiarities of structure were indeed 

 found to be so' universally present in mountain chains, 

 that no range of hills was deemed worthy of that title 



1 " Report on the Geology of the Henry Mountains." By G. K. Gilbert. 

 •1. 1877.) 



