388 



NA TURE 



[February 22, 1894 



depended on the medium. Of course the same view is even 

 more universally held to-day. 



All this might, however, have been passed over as an " indis- 

 cretion de jeunesse " if M. Mercadier had not in June last made 

 the extraordinary claim to have proved on such a basis of argu- 

 ment and experiment that the electromagnetic system of units 

 has a theoretical justification which the electrostatic system 

 lacks. 



In this recent paper the notation is changed, and k' is used 

 for l/ju. Here again the invariability of this quantity in non- 

 mr.gnetic materials is used as an argument to prove that it does 

 not depend on the nature of the medium. 



For the rest M. Mercadier develops certain mixed systems 

 of dimensions, which I need not discuss. 



In answer to his complaint that I omitted to notice his 

 memoir in a paper which I wrote on the same subject in 1889, 

 I wish to point out that I did not then enter upon the biblio- 

 graphy of the subject. I regarded myself as dealing with a 

 theory well understood by experts, and as advocating a change 

 in notation chiefly for the benefit of less advanced teachers and 

 students. The considerations advanced were direct deductions 

 from Maxwell's theory. That theory was more generally under- 

 stood in 1889 than when the discussion in the Philosophical 

 Magazine took place in 1882, and since the latter date the 

 practice ofretainingK and /i in dimensional formulae is spreading. 



As far, however, as M. Mercadier's papers of 1883 were cor- 

 rect, the ideas ihey embodied had been explicitly stated in the 

 Philosophical Magazine some months before. As far as they 

 went beyond that point, by the attempt to discriminate between 

 the theoretical validity of the electrostatic and electromagnetic 

 systems, the arguments adduced were quite unsound. 



Arthur W. Rt cker. 



Royal College of Science, South Kensington, 

 February 5. 



The Cloudy Condensation of Steam. 



Mr. Aitken's letter (p. 340) shows that he has curiously mis- 

 understood me. I never entertained the smallest "objection 

 to" his "not countenancing the nucleus theory to explain " the 

 action of electricity upon the steam jet. On the contrary I was 

 rejoiced to find that so able and distinguished a physicist 

 appeared to hold the same opinion on this point as myself. In 

 labouring to abbreviate I must have become very obscure. Per- 

 haps my meaning may be made clearer by an amplified and 

 annotated paraphrase of the words in question (see ante p. 

 213). 



After trying to show that dense condensation takes place only 

 when there is an actual discharge of electricity, which, however, 

 need not necessarily electrify the jet, I go on : " The inference 

 clearly is that in some way or other the action is brought about 

 by the air in which electrical discharge has taken place, and 

 not directly by the electricity itself. Since so much has been 

 said in the earlier part of the lecture about the influence of dust 

 in promoting condensation the [erroneous] idea has, no doubt, 

 occurred to many of you that in the present case also the air 

 owes its condensing power to the fact that it has become 

 charged with dust. [The great majority of the many scien- 

 tifically educated people to whom I have at different times 

 shown the experiment at once made this suggestion.] Minute 

 particles are indeed torn off the electrodes by the 

 discharge and [you may think] form nuclei upon 

 which the steam condenses. This [mistaken] hypothesis 

 seems at first sight to be favoured by the experi- 

 ments of Liveing and Dewar, and by the well-known fact 

 that burning touchpaper induces condensation ; it also has the 

 support of Prof. Barus, who appears inclined to think that 

 such condensation is in all cases due to the action of small 

 particles of matter. On the other hand, it is noteworthy that 

 Mr. Aiiken, who knows more about the condensing property of 

 dust than any man living, gives no countenance to the nucleus 

 theory as explaining the action of electrical discharge upon the 

 steam jet. The possibility of such an explanation must 

 necessarily have presented itself to the mind of one so familiar 

 with the subject, and since he does not make the slightest 

 allusion to it, I imagine that his experiments have led him to 

 the conclusion that it is untenable. This affords me great satis- 

 faction, inasmuch as my own experiments have led me to the 

 same conclusion — not only as regards the action upon the 



NO. 1269, VOL. 49] 



steam jet of electrical discharge, but also of burning matter."' 

 [I did not intend to imply, though the words of the abstract 

 apart from the context unfortunately seem to bear that meaning, 

 ihat Mr. Aiiken thought the action of burning waiter was not 

 due to nuclei, but that I myself thought it was not.] Then 

 follows an account of experiments tending to show that the air 

 does not derive its power of condensing the steam jet from dust 

 but from dissociated atoms. 



The above will, I hope, convince Mr. Aitken that^ except 

 perhaps as regards one slipshod sentence, which I regret having 

 overlooked when correcting the proof, he has no cause to feel 

 agijrieved. I am confident that my hearers never for a 

 moment understood me to say that he had abandoned one iotaj 

 of his conclusions regarding the action of dust, but merely that 

 he did not consider the dust-nucleus theory applicable to the 

 case of the electrified steam jet. 



I believe that I am well acquainted with all Mr. Aitken's 

 papers on the subject of condensation, but I do not remember 

 the experiment with the polished ball referred to in his letter. 

 Perhaps it is an unpublished one. The experiments which he 

 mentions in his final paragraph, relating to the condensation 

 caused by certain acids, were made upon water-laden air con- 

 tained in closed vessels, and not upon the steam jet. The con- 

 ditions in the two cases are very different, so much so that, for 

 i example, liydrochloric acid, which in the steam jet is the most 

 active source of dense condensation that I have met with, was- 

 I found by Mr. Aitken (he will pardon me for reminding him) to 

 j form no foggy condensation at all in a receiver of moist filtered 

 I air ; while ordinary dusty air, which exerts such a powerful 

 : action in the closed vessel, fails to produce any sensible effect 

 j when introduced into the open steam jet. 

 I Shelford Bidwell. 



Southfields, Wandsworth, February 11. 



On the Cardinal Points of the Tusayan Villagers. 



In the second volume of the yournal of American Ethnology 

 and Archicology I have pointed out, for the first time, that the 

 four cardinal points among the Tusayan villagers are not the 

 same as those of the astronomers, or that their north is approxi- 

 mately north-west. I also gave, in the same article, tables with 

 the amount of the angular variations, showing that the sacred 

 rooms, or kivas, where the mysteries of their ceremonial worship 

 are performed, are oriented, riiughly speaking, in accordance- 

 with their conception of the positions of north, west, south and 

 east. It was shown that the amount of angular variation was 

 constant, and later, in a description of the ruins of A-na-to-bi, 

 the same orientation was made known. 



In an article published in the December number of the 

 yournal of American Folk Lore, it was stated by me that the- 

 cardinal points among these aborigines are determined by the 

 solstitial risings and settings of the sun. 



The publication of Piof. J. Norman Lockyer's work on 

 "The Dawn of Astronomy," in which the orientation of 

 certain of the sun-temples in the Nile valley and elsewhere in 

 the old world is referred to solstitial points in the horizon, gives 

 a new interest to these observations among the aboriginal house- 

 builders and their descendants in America. 



Since the publication (1892) of my observations on the 

 orientation of Tusayan (Moki) kivas and its relationship to 

 solstitial points of sunrise and sunset, I have examined the 

 scanty data which we have regarding the orientation of temples 

 in Central American ruins, and have unearthed significant facts 

 bearing on this question, as well as that of the kinship of the 

 Pueblo people and those who once inhabited the "cities" of 

 Mexico, including Yucatan. Evidences of relationship between 

 the aboriginal housebuilders of Arizona and New Mexico, and 

 those of Nahuatl and Maya stocks have elsewhere been pre- 

 sented. It seems to me that the above observations made in 

 1891, quite independently of the discoveries of Lockyer on the 

 orientation of temples in the old world, in the light of his dis- 

 cussion, open a field of research in the archaeology of the house- 

 builders of Central America which is sure to lead to interesting 

 discoveries. J. Walter Fewkes. 



Boston, Mass., U.S.A. 



The Scandinavian Ice-sheet. 



Many geologists affirm that the Scandinavian ice-sheet 

 became confluent with that of Scotland, and reached the East 



