8o 



NA TURE 



[May 25, 1882 



traversed, are of much interest. The work is well sup- 

 plied with good maps, and has a number of good and 

 useful illustrations. It is well worth reading. 



LETTERS TO THE EDITOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can lie undertake fa return, 



or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 

 [ The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible othinvise to ensure the appearance even 

 0/ communications containing interesting and novel facts.} 



Dr. Siemens' Solar Hypothesis 

 I HAVE been waiting for several weeks for answers to the 

 following rather obvious objections to Dr. Siemens' Solar Hypo- 

 thesis, but I have not seen them either ashed by others or 

 answered by Dr. Siemens. 



1. How the' interplanetary gases near the sun acquire a suffi- 

 cient radial velocity to prevent their becoming adense atmosphere 

 round him ? 



2. Why enormous atmospheres have not long ago become 

 attached to the planets, notably to the moon ? 



3. Why the earth has not long ago been deluged when a con- 

 stant stream of aqueous vapour that would produce a rain of 

 more than 30 inches per annum all over the earth must annually 

 pass out past 1 he earth in order to supply fuel to be dissociated 

 by the heat that annually passes the earth ? 



4. Why we can see the stars although most of the solar radia- 

 tions are absorbed within some reasonable distance of the sun ?. 



Geo. Fras. FitzGeralu 

 40, Trinity College, Dublin, May 16 



I have the pleasure to reply to the very pertinent questions 

 put by Prof. FitzGerald as follows : — 



1. The gases being for the m .st part hydrogen and hydrogen 

 compounds have a low specific gravity as compared with the 

 denser ga-es forming the permanent solar atmosphere. On 

 Hashing into flame in the photo-phere, their specific gravity would 

 be vastly diminished, thus giving rise to a certain rebound action 

 which coupled with their acquired onward motion, and with the 

 centrifugal impulse they receive by fictional contact with the 

 lower atmosphere, constitutes them a surface stream flowing from 

 the polar to the equatorial regions, and thence out into space. 

 (Lest I should be misunderstood, allow me to add that 1 do not 

 look up m centrifugal action as sufficing in any way to overcome 

 solar gravitation.) Astronomers are in the habit of regarding 

 each spheroid possessed of an atmophere as rotating in vacuous 

 space ; under such circumstances the atmosphere must partake 

 of the rotatory moti m of the solid spheroid, and after having 

 attained an increased depth at the equator, will assume a state 

 of static equilibrium unless disturbed by external influences. No 

 such statical equilibrium is pos ible, however, if we assume the 

 same spheroid with its atmosphere, surrounded by an ocean of 

 indefinite dimensions, consisting of ga eous matter not partaking 

 of the rotation of the spheroid, although subject to its attractive 

 influence. Equal masses will under those conditions be equally 

 attracted both in the polar and equatorial direction, and the con- 

 tinued disturbance of equilibrium by rotatory motion must result 

 in continuous outflow. Nor need this outflow be accomplished 

 entirely at the expense of rotato'y motion of the spheroid because 

 (he bill iwing polar current when once established, will only have 

 to be changed in direction by factional action in order to convert 

 it into the outflowing current. 



2. Regarding the -econd question, I assume that the atmo- 

 sphere of each spheroid in space is precisely such as would 

 result from its mas, and if this view is correct, the moon also 

 must ha\c an atmosphere, though of so attenuated a character as 

 to be scarcely perceptible by means of optical instruments ; for 

 as Wollaston put it in his celebrated paper, read before the 

 Royal Society in January 1S22, "it would not be greater than 



111 atmosphere is, where the earth attraction is equal to 

 that of the moon at her surface, or about 5000 miles from the 

 earth's surface.'' I am well aware thai in assuming atmospheric 

 air to lie a perfectly elastic fluid, the atmospheric density would 

 at a height of only 70 kilometers not exceed the I -7000th 1 art of 

 1 [iy, and would therefore at greater d'S'ances 



bi come inappreciable ; but we have evidence to show that Boyle 

 and Mariotte's law holds good only within comparatively narrow 

 limits, and there is other evidence referrW to in my paper in 

 favour of the supposition that such gases as are contained in 

 meteorites are diffused through sprace in appreciable amounts, or 

 the meteorites could not for millions of years have retained these 

 gases, notwithstanding the action of diffusion into empty space. 



3. The amount of vapour that would condense upon the earth 

 under the conditions here assumed, would depend upon its mean 

 temperature on the one hand, and on the vapour-density of the 

 stellar atmosphere surrounding it on the other. Assuming the 

 density of the stellar atmosphere, which, while surrounding th*? 

 earth does not partake of its rotatory motion to be I ■ 10,000th part 

 of atmospheric density, and saturated wdth aqueous vapour, the 

 point of condensation would be according to Regnault - 50° C, 

 if the outer regions of our atmosphere should be at that tempera- 

 ture, and saturated with aqueous vapour, the two would be in 

 diffusive balance ; if they were at a lower temperature they would 

 acquire, and if at a higher they would part w ith aqueous vapour 

 to the surrounding medium. 



4. It has long been held by astronomers that there are stars 

 beyond our lange of vi-ion, which hypothesis would involve that 

 of absorption of heat and light rays in stellar space ; some rays 

 are more easily absorbed than others ; thus it ap| ears to be the 

 yellow rays which are most efficacious in the decomposition of 

 carbonic acid and aqueous vapour in the vegetable cell. May 

 not the a ne conditions prevail in space, and allow probably the 

 rays of highest refrangibility to pass on to the greatest distance 

 w itbout being absorbed— I should say utilised — in doing chemical 

 work? C. Wm. Siemens 



12, Queen Anne's Gate, S.W., May 22 



Porculia Salvania (Hodgson) 

 A MOST valuable and interesting addition has recently been 

 made to the Zoological Society's collection in Regent's Park, of 

 four— a male and three females — Pigmy Hogs (Porculia sal- 

 vania, of Hodgson) from the Doars of Bhotan. The extreme 

 rarity and difficulty of procuring this animal makes its pre- 

 sence here of the greatest interest, and these individuals will 

 be examined eagerly, not only by naturalists, but by many 

 Indian travellers, sportsmen, and others, who have heard of, but 

 never had the opportunity of seeing the pigmy hog. My atten- 

 tion was directed to it many years ago by the late Mr. Blyth, 

 then in Calcutta, who on my first expedition to the Nepaul 

 Terai, in 1855, requested me to endeavour to obtain a speci- 

 men — as far as I remember, neither Blyth nor Jerdon had seen it 

 living — Hodgson, who described and named it, had heard of 

 its existence from the Nepalese or other denizens of the Terai, or 

 neighbouring localities, long before he obtained a specimen. I 

 was unable to procure one, though I made repeated attempts to 

 do so, and enlisted many influe tial friends in the search, but 

 without success ; very few appeared to know even of its exist- 

 ence, whilst many seemed to regard it as mythical. Occasion- 

 ally I met with natives who said they had heard of it, but I beg 1 11 

 to fear that it might be extinct. The four fine specimens now 

 in the Gardens prove that such is not the case, and will furni h 

 opportunity of supplementing Hodgson's description of the ani- 

 mal, which is to be found in the Proceedings of the Zoological 

 Society, and in Jerdon's "Mammals of India." 



These lively little pigs, weighing probably hardly as much as a 

 hare, are most active and energetic ; they resemble the ordinary 

 pig in miniature, but probably may have some anatomical pecu- 

 liarity which will interest naturalists as regards affinity with the 

 Peccaries. The specific designation Salva ia, is from the S il 

 (Shorea A'obttsta), as the pig is, I believe, found in that part of 

 the Terai and along the sub-Himalayan tracts, where the Sal tree 

 abounds, and among the long gra-s in which the little creatu e 

 hides it-elf. It is much to be hoped that they will breed, and 

 thus enable other zoological collections to be supplied wi h 

 specimens of a most rare and interesting species. 



J. Fayrer 



Pseudo-Glacial Phenomena 



I beg to call the attention of geologists to the following 



facts: — On the north-east coast of Australia, at the end of 



Trinity Pay, about lat. 17° S., there are sleep ranges of granite 



abulting o 1 the sea-margin. Every rainy season (December, 



'il February) imme.ise quantities of the granite 



