248 



THE POPULAR SCIENCE MONTHLY. 



forms, is insignificant when compared with that 

 which has been absorbed during the decomposi- 

 tion of silicated rocks and is now fixed in the 

 form of limestones. The magnitude of this 

 process is seen when we consider that all the 

 argillaceous rocks and clays of the stratified 

 formations have come from the decay of the 

 feldspars and other silicates of the earlier eozoic 

 terrenes through the intervention of carbonic 

 acid, and that the resulting alkaline and earthy 

 carbonates are now represented by the lime- 

 stones so abundant in the earth's crust. It was 

 shown, in the author's communication already 

 quoted, that a layer of pure limestone covering 

 the earth's surface to a depth of about twenty- 

 eight feet (8.61 metres) corresponds to an 

 amount of carbonic acid which, if set free, 

 would double the weight of the present atmos- 

 phere, and the existence of great limestone 

 and dolomite formations, many hundred feet in 

 thickness, at different geological horizons over 

 wide areas, will, it is believed, justify the con- 

 clusion that the earth's crust contains, fixed in 

 the form of carbonates, an amount of carbonic 

 acid which, if liberated in a gaseous form, would 

 be equal in weight to at least two hundred at- 

 mospheres like the present one. A portion of 

 this carbonic acid was doubtless separated at an 

 early period in the history of our globe, since 

 the limestones of eozoic rocks are of consider- 

 able thickness, and those of more recent times 

 are in part derived from the solution and re- 

 deposition of the older limestones. The only 

 known source of carbonic acid, apart from com- 

 bustion and respiration, are certain terrestrial 

 exhalations of the gas, probably due to chemical 

 reactions liberating small portions which had 

 long before been fixed in the form of carbonates. 

 We are thus forced to one of two conclusions : 

 either the wholly improbable one that the at- 

 mosphere, since the appearance of organic life 

 on the earth, has been one of nearly pure, car- 

 bonic acid, and of such immense extent that the 

 pressure at the surface would have sufficed, at 

 ordinary temperatures, for its liquefaction ; or 

 else, the atmosphere being so constituted as to 

 permit vital processes, that carbonic acid, as 

 fast as removed by chemical action at the earth's 

 surface, was supplied from some extra-terres- 

 trial source. We may, in accordance with this 

 last hypothesis, admit that the atmosphere is 

 not terrestrial but cosmical, and that the air, 

 together with the water surrounding our globe 

 (whether in a liquid or a vaporous state), be- 

 longs to a common elastic medium, which, ex- 

 tending throughout the interstellary spaces, is 

 condensed around attracting bodies in amounts 

 proportional to their mass and temperature, 

 while in the regions most distant from these 

 centres of attraction this universal atmosphere 

 would exist in the state of greatest tenuity. 

 Such being the case, a change in the atmos- 

 phere of any globe, whether by the absorption 

 or disengagement of any gas or vapor, would, 

 by the laws of diffusion and of static equilib- 

 rium, be felt everywhere throughout the uni- 

 verse ; and the fixation of carbonic acid at the 

 surface of our planet would not only bring in a 



supply of this gas from the worlds beyond, but, 

 by reducing the total amount of it in the uni- 

 versal atmosphere, would diminish the atmos- 

 pheric pressure at the surface of our own and 

 of other worlds. 



" This hypothesis is not altogether new. Sir 

 William R. Grove, in 1842, put forth the notion 

 that the medium of heat and light may be 'a 

 universally diffused matter,' and, subsequently, 

 in 1843, in his celebrated ' Essay on the Corre- 

 lation of Physical Forces,' in the chapter on 

 Light, concludes, with regard to the atmosphere 

 of the sun and the planets, that there is no 

 reason why these atmospheres k should not be, 

 with reference to each other, in a state of equi- 

 librium. Ether, which term we may apply to 

 the highly-attenuated matter existing in the in- 

 terplanetary spaces, being an expansion of some 

 or all of these atmospheres, or of the more vol- 

 atile portions of them, would thus furnish mat- 

 ter for the transmission of the modes of motion 

 which we call light, heat, etc., and possiby 

 minute portions of these atmospheres may, by 

 gradual accretions and subtractions, pass from 

 planet to planet, forming a link of material com- 

 munication between the distant monads of the 

 universe.' Subsequently, in his address as Pres- 

 ident of the British Association for the Ad- 

 vancement of Science, in 18G6, Grove further 

 suggested that this diffused matter might be a 

 source of solar heat, inasmuch as the sun may 

 'condense gaseous matter as it travels in space, 

 and so heat may be produced.' " 



Pottery: How it is made, its Shape and 

 Decoration. With a Full Bibliography 

 of Standard Works upon the Ceramic Art, 

 and 42 Illustrations. By George Ward 

 Nichols. New York : G. P. Putnam's 

 Sons. Pp. 142. Price, $1.25. 



This seems to be a useful little manual, on 

 a subject that is now attracting a good deal 

 of attention. It is elegantly illustrated and 

 beautifully printed, and it will be especially 

 prized by many on account of its copious 

 bibliography of the principal works upon 

 the ceramic art. The volume is thus char- 

 acterized by the author, in a few words of 

 preface : 



" It is the object of this book to show that the 

 manufacture of pottery may become one of the 

 great art-industries in the United States ; to de- 

 scribe the laws which govern the form and 

 decoration of pottery; and to give practical 

 instruction in the art of painting, either with 

 vitrifiable or common oil colors, upon hard or 

 soft porcelain, or upon earthenware. It is the 

 result of long and careful study, and is intended 

 not only for the benefit of professional potters 

 and decorators, but for that large class of per- 

 sons who are seeking to acquire this art, either 

 for entertainment or as a remunerative occupa- 

 tion." 



