Sept. 22, 1882.] 



♦ KNOWLEDGE 



281 



alas ! to how many sources of error is this method exposed. If the 

 potash has been in contact with any organic substance, it will 

 absorb oxygen. If the pumice that takes the place of the potash 

 contains protoxide of iron, it will also absorb oxygen. In both cases, 

 the oxygen increases the weight of the carbonic acid. 



Every experimenter who has been compelled to repeat the 

 weighing of a somewhat complicate piece of apparatus, with an 

 interval of several hours between, knows how many inaccuracies he 

 is exposed to if he is compelled to take into calculation the changes 

 of temperature and pressure, and the moisture on the surface of 

 the apparatus. After fighting all these diificulties, and frequently 

 in vain, the experimenter begins to mistrust every result that 

 depends only on difference in weight, and to prefer those methods 

 whereby the substance to be estimated can be isolated, so that it 

 can be seen and handled, weighed or measured, in a free state, and 

 in its own natural condition. 



The classical experiments of Thenard, of Th. de Saussnre, of 

 Messrs. Boussinganlt, on the quantity of carbonic acid in the air, 

 are well known to every one ; they need only to be organised, 

 repeated, and multiplied. 



J. Reiser, who has conducted a long and tedious series of expe- 

 riments on this subject, has adopted a process that seems to offer 

 every guarantee of accuracy. The air that furnishes the carbonic 

 acid is aspirated through the absorption apparatus by two aspira- 

 tors of 6U0 litres capacity. The temperattire and pressure of the 

 air are carefully measured. The carbonic acid is absorbed by- 

 baryta water in three bulb apparatus. The last btilb, which serves 

 as a check to control the operation, remains clear, and proves that 

 no binoxide of barium is formed. The baryta water used is titrated 

 before and after the operation, and from the difference is calculated 

 the quantity of carbonate formed, and hence of the carbonic acid. 



These tedious experiments, which varied in duration from 6 to 

 25 hours, require at least two days of continuous labour. They 

 were repeated 193 times by Keisec in 1872, '73, and '79. They were 

 made in still weather, and in violent winds and storms. The air 

 was taken at the sea-shore, in the middle of the fields, on tlie level 

 earth, during harvests, in the forests, and in Paris. Under such 

 varied conditions, the quantity of carbonic acid varied but little; 

 the numbers obtained were between 294 and 31. which may be 

 taken as a general average of the carbonic acid in the air. 



The quantity of carbonic acid in the free atmosphere is tolerably 

 constant, which must necessarily be the case according to 

 Schloesing's proposed relation between the bi-carbonate of lime in 

 the sea and the carbonic acid in the air. The only cause that seems 

 at all competent to change the geological quantity of carbonic acid 

 in the atmosphere is the formation of fog. As the aqueous vapours 

 condense, they collect the carbonic acid ; and the foggy air, as a 

 rule, is more heavily laden with this gas than ordinary air. 



It is not surprising that there is less carbonic acid in the air 

 collected on clear summer days, in the midst of clover, Ac, that is in 

 an active reducing furnace ; if anything is surprising, it is that the 

 quantity of carbonic acid does not sink below 28, 



It is also a matter for surprise that in Paris, among so many 

 Eonrces of carbonic acid, the furnace fires, the respiration of men 

 and animals, and the spontaneous decomposition and decay of 

 organic substances, the quantity of carbonic acid does not 

 exceed 3o. 



If, theu, the great general mean of normal atmospheric carbonic 

 acid deviates but little from 29 or 30, it is not doubtful that under 

 local conditions, in closed places, and under exceptional meteoro- 

 logical conditions, considerable variations may occui- in these pro- 

 portions. But these variations do not affect the general laws of the 

 composition of the atmosphere. 



There are two entirely distinct points from which the measure- 

 ment of the atmospheric carbonic acid may be contemplated. 



The first consists in considering it as a geological element which 

 belongs to the gaseons envelope of the earth in general, and it leads 

 us to express the general relation of c-arbonic acid to the quantity of 

 air, as about three volumes in lO.OCH). 



The second, which relates to accidental and local phenomena, to 

 the activity of man and beast, to the effect of fires and of decom- 

 posing organic matter, to volcanic emanations, and finally to the 

 action of clouds and rain, permits us to recognise the changes 

 which can occur in air exposed to the influences mentioned, and to 

 a certain extent confined. Without denying that it is of interest 

 from a meteorological and hygienic standpoint, it does not take the 

 same rank as firsfa 



J. Reiset's experiments, by their number, accuracy, the large 

 volumes employed, and the interval of years that separate them, 

 have definitely established two facts on which the earth's history 

 must depend : the first is, that the percentage nf carbonic acid in 

 the air- scarcely changes ; the second, that it differs but little from 

 To?,7ru hy volume. 



These results are fully confirmed by the results which were ob- 



tained by Franz Schulze, in Rostock, in 1868, 'C9, '70, and '71. The 

 averages which he got, with very small variation, were 2-86G8 for 

 1809, 2-9052 for 1870, and 30126 for 1871. 



More recently Muontz and Aubin have analysed air collected on 

 the plains near Paris, on the Pic du Midi, and on the top of Pny- 

 dc-Dome. Their results agree -with those published by Reiset and 

 Schulze. 



The grand average of carbonic oxide in the air seems to be 

 tolerably fixed, but after this starting-point is established it 

 remains' to study the variations that it is capable of, not from local 

 causes, which are of little importance, but from general catises con- 

 nected with large movements of the air. Upon this study, which 

 demands the co-operation of a definite number of observers 

 stationed at different and distant points of the earth, the experi- 

 ments being made simultaneously and by comparable methods. 



M. Dumas called the attention of the Academy to this point, in 

 connection with its mission of selecting suitable stations for 

 observing the transit of Venus. The process and apparatus of 

 Muentz and Aubin offer the means adapted for making these 

 experiments, and seem sufficient to solve the problem which science 

 proposes, of determining the present quantity of carbonic acid in 

 the air. 



If these experiments yield satisfactory results, as we have good 

 reasons to believe they" will, it is to be hoped that annual observa- 

 tions will be made in properly-chosen places, so as to determine the 

 variations which may possibly take place in the relative quantity of 

 atmospheric carbonic acid during the coming century. — " Compt. 

 Rend.," p. 589. 



[Although this proposition was made by a Frenchman to ma 

 fellow scientists, would it not be well for some American to accept 

 the challenge, and bring it before the coming meeting of the 

 American Association for the Advancement of Science, in the hope 

 that we too may contribute our mito of effort in the same direc- 

 tion ? — Ed.] 



Ancient Moxuitexts. — The following are the antiquities to which, 

 so far as England and Wales are concerned, the Government Bill 

 for the better protection of ancient monuments applies. In 

 Anglesey, the tumulus and dolmen, Plas Xewydd ; in Berkshire, 

 the turnulus Wayland Smith's forge, and Uffington Castle ; in 

 Cumberland, the stone circle Long Meg and her daughters, near 

 Penrith, the stone circle on Castle Rigg, near Keswick, and the 

 stone circles on Burn Moor; in Derbyshire, the stone circle, the 

 Xine Ladies on Stanton Moor, the tumulus Arbor Low, Hob Hurst's 

 house and hut on Bastow Moor, and Minning Low in Glamorgan- 

 shire, Arthur's Quoit, Gower ; in Gloucestershire, the tnmulas 

 at Uley ; in Kent, Kit's Coty-house ; in Northamptonshire, Danps' 

 Camp and Castle Dykes ; in Oxfordshire, the Rollrich Stones; in 

 Pembrokeshire, the Pentre Evan Cromlech; in Somersetshire, the 

 ancient stones at Stanton Drew, the chambered tumulus at Stoney 

 Littleton, Wellow, and Cadbnry Castle; in Westmoreland, May- 

 borough, near Penrith, and Arthur's Round Table at Penrith ; in 

 Wiltshire, Stonehenge, Old Sarum, the Vallum at Abury, the sarcen 

 stones within the same, those along the Kennet-road, the group 

 between Abury and Beckhampton, the long barrow at West 

 Kennet, near Marlborough, Silbury-hill, the Dolmen (Devil's Den), 

 near Marlborough, and Barbnry Castle. 



Electric R.uiwats. — The development of electric railways and 

 tramways is now considerable. Putting aside numerous lines that 

 are merely talked of or projected, those which are working, autho- 

 rised or in course of construction, show a total length (according to 

 the Revue IndustrieUe, July 19) of 160 kilomiMres— i.e., abont 100 

 miles, and grants are becoming even more numerous. The lines 

 actually at work are those of Lichterfelde (about 26 kilometres in 

 length), and that from the Spandaner Rock to Charlottonbcrg, near 

 Berlin ; another line, from Port Rush to Bush Jlills, in the north 

 of Ireland, has been inaugurated (length about 10 kilomJtres), 

 and also in Holland, one from Zandvoort to Kostverl.iren Oongth 

 a little over two kilometres). Among lines authorised or in 

 construction, the folio-wing aro noted :— In Austria, the Moedling 

 line, near Vienna (2t kilometres), to bo constructed by the Southern 

 Railway Company there. In Germany, the line from Wiesbaden to 

 Niirnberg (two kilomitres), and tha't from the Roynl mines of 

 Saxony to Zankerode. In England, a line under the Thames, con- 

 necting Charing-cross and Waterloo Stations (1'2 kilometres) ; also 

 a line in South Wales (60 kilometres), for which the force will be 

 derived from fall of water. In Italy, Turin, and Milan will soon 

 begiu the construction of electric tramways. In America the 

 Ellison Company have arranged for the working of SO kilometres 

 on one of tho great lines from New York. Another small line 

 (1-8 kilometres) is to be made at St. Louis, in Missouri, by Mr. 

 Eeisler. 



