522 



NA TURE 



[Makch 30, 1899 



Variatum of Viscosity with Temperature. 



In order lo apply the method to the measurement of extreme 

 temperatures, it is not suflicient to be able to measure resistance. 

 It is also necessary to determine the law of the variation of 

 viscosity with temperature. Here, again, recourse must be had 

 to the method of extrapolation. Fortunately, in the present 

 instance, the temperature can be measured through a very wide 

 range, and the range of extrapolation, being limited by the 

 melting point of platinum, is not very great in comparison. It 

 should be possible therefore, by sufficiently varying the con- 

 ditions of the experiments, and by comparing the behaviour of 

 different gases throughout the whole range of temperature, to 

 arrive at a very fair degree of certainty with regard to the 

 essential nature of the phenomenon. Owing lo want of leisure 

 for the work, the author's experiments have not as yet extended 

 over a sufficient range of temperature, except in the case of air, 

 to warrant the publication of any general conclusions with 

 regard to the law of variation of viscosity, or of any results at 

 high temperatures obtained by the method of extrapolation. It 

 may be stated, however, that the formula above quoted, accord- 

 ing to which the viscosity varies as some power h of the 

 temperature, though f;iirly exact over a moderate range of 

 temperature, fails entirely when tested at higher points. The 

 results of Obermayer appear to be the most accurate for the 

 different gases between 0° and 100" C, but if the same formula 

 is retained, the value of the index n diminishes as the temper- 

 ature is raised. Taking the average value between 0° and 100° 

 for air as being 076, the value falls to 070 between 100° and 

 450°. A result of this nature was found by Wiedemann, but the 

 rate of diminution which he gives appears to be far too great. 

 He gives, for instance, the value it = o'67 fo"r air between 0° 

 and 184°, which implies a rate of diminution of the index many 

 times greater than that which actually occurs. It would be very 

 difficult by the method which he employed to make sure al any 

 deviation whatever from the formula over so small a range, and 

 since the error of his determination is much greater than that 

 of the formula, he can hardly be said to have disproved the 

 index law. 



The problem is seriously complicated by the failure of the 

 .simple formula ; but since the measurements are capable of 

 great exactitude, and since it is possible to obtain many in- 

 dependent checks by comparing the results of the two methods 

 of effusion and transpiration, and also by examining the behaviour ' 

 of different gases, the author is confident of ultimate success. 

 The method of experiment here described has already led to 

 many promising and interesting results, and it is probable that 

 the complete solution of the problem when attained, besides 

 leading to more accurate determinations of extreme temper- 

 atures, may also throw light on dissociation and on many 

 other points which are at present obscure in the theory of 

 gases. 



CENTRAL AMERICAN ARCH.KOI.OGY} 

 /~\WING to difficulties raised by the Honduras Government, 

 ^-^ the directors of the I'eabody .Museum have unfortunately 

 been obliged, since the year 1895, ''^ suspend work at the ruins 

 of Copan, and Mr. Gordon, the leader of their expeditions in 

 Honduras, was directed to turn his attention to other points of 

 antiquarian interest in the neighbourhood. His reports to the 

 Museum are now published. 



In April 1896, and June 1S97, an examination was made of 

 some caverns which had been discovered in the limestone cliffs 

 rising .abruptly from the rocky bed of a mountain stream, distant 

 about four miles from the ruins of Copan. The nature of the 

 ground m.ade the entrance of the caves very ditricult and some- 

 what dangerous of approach. 



In one of the chambers, nearly circular in shape and 

 mea.suring 150 feet in diameter, "an excavation 20 feet long 

 and 3 feet wide was made. After the surface layer of dust 

 came a thin crust, which must have been caused by the presence 

 of moisture at some period. It was only a few inches in 

 thickness, and beneath it the material was very dry, soft, 

 and loose, so that the men were able to remove it easily 

 without the use of picks. In the surface crust and beneath it 



1 " Memoirs of the Peabody Museum of American Archjcology .-ind 

 Ethnologv, Harvard Univcrsily," Vol. i., Nos. 5-*. Rcsc.irclics in Ihc Uloa 

 Valley, Honduras ; Caverns of Copan, Honduras. Hy Ceorge llyron 



NO. 1535, VOL. 59] 



lo a depth of three feet were found ashes, charcoal, and pot- 

 sherds. The latter are not numerous, and are of a coarse 

 quality. .-\t a depth of three feet the potsherds and ashes and 

 all signs of occupation disappeared ; the material excavated 

 grew lighter in colour, softer and looser. In appearance and 

 behaviour it resembled quicklime, of which it largely consisted. 

 Throughout the whole excavation the material removed ro.se in 

 the air in thick clouds of suff^ocating dust. The excavation was 

 carried to a depth of fifteen feet, where the bottom of the cavern 

 was reached in part of the excavation. On the rock floor were 

 absolutely no traces of occupation." 



In a long passage, measuring about 80 by 20 feet, where the 

 floor .seemed to be more uneven than in the other chambers, and 

 gave way to the pressure of the feet with a crushing sound, Mr. 

 Gordon discovered that he was walking over the crumbling 

 human bodies mingled with ashes and lime. A ma,ss of charred 

 and calcined bodies occupied the entire floor to the depth of 

 about two feet, and the thick clouds of unsavoury dust, added to 

 the stifling he.at, made the work of examination most difficult 

 and disagreeable, The chamber appears to have been used as a 

 place for depositing the remains after they had been ]>artly 

 cremated elsewhere. None of the caves show any signs of 

 recent occupation, but the condition of bones and of a svooden 

 object, which was discovered, do not seem to Mr. Gordon to 

 indicate any great antiquity. The excavations yielded no 

 specimens of personal ornaments, or of carved stonework, and 

 the pottery, of which several pieces were preserved entire, 

 proved to be entirely different in character from that found in 

 the neighbouring ruins of Copan. Mr. Gordon does not, how- 

 ever, think that the facts disclosed from the examination of the 

 caves suffice to prove the existence of another race. " May it 

 not be," he says "(to hazard a guess), that these cave relics 

 belong, after all, to the same period as Copan itself, and are 

 remains of the Copan people, or the devotees of some old cult 

 among them whose temples were the caves, and whose vessels 

 used in the ritual were of a design and character exclusively 

 their own ?" 



In May and June 1896, and from March to June 1897, Mr. 

 Gordon was occupied in examining the valley of the Uloa 

 River, which flows northward through a forest -covered plain to 

 the Gulf of Honduras. Above ground only a few vestiges of a 

 former population are to be found, and the principal group of 

 mounds, which was examined, yielded only one example of 

 sculpture— namely, a very rough stone idol similar to the rude 

 stone sculptures found in Nicaragua. However, during the rainy 

 season the river cuts into its banks, and frequently leaves exposed 

 to view cross sections of unconsolidated strata of s.and and clay 

 about thirty feet in height, which in some cases '■ present the 

 continuous spectacle of broken pottery and fragments of bone 

 from the surface of the water to within a few (eet of the top. 

 In places these objects are very numerous for stretches of 

 several hundred feet, then diminishing gradually and almost 

 disappearing for miles." 



The principal excavations were made near the village of 

 Santana, about twenty-five miles in a straight line from the 

 mouth of the river. The objects found, consisting chiefly of 

 fragments of pottery, were met with in distinct layers a few feel 

 in thickness, separated by other layers, which also contained a 

 few objects, but in much smaller numbers. In e.xcavation 

 No. 3, for in.stance, there were three principal layers at depths 

 of twelve, twenty, and twenty-five feel ; the last, in this case, 

 by far the most extensive of the three. The pottery shows no 

 signs of water-wearing, and it seems probable that the various 

 articles "must have been put underground in the customary way 

 in connection with burials, but not to the depth at which they 

 are found at present. These burials must have been made 

 during successive periods of occupation, .separated by a series of 

 inundations, each of which raised the general level of the 

 ground several feet by the deposition of detritus from the 

 mountains." 



I'rom an examination of the large collections which were 

 made, Mr. Gordon is of opinion that the natives of this valley 

 had attained a proficiency in the art of pottery not exceeded in 

 any other part of Central America, and although the specimens 

 display great variety in char.acter, it is evident that the dominant 

 influence was .Maya. The absence of architectural remains, the 

 most familiar and remarkable feature of Maya culture in other 

 regions, he attributes to the absence of any available supply of 

 building-stone in the valley of the Uloa. 



" It IS among the pottery vessels that the Maya affinities are 



