January 12, 1922] 



NATURE 



59 



no inconvenience. The analyser can be rotated about 

 the axis of the microscope, and is provided with clicks 

 in the positions of crossed and parallel nicols. There 

 is an arrangement by which it can be rotated altern- 

 ately through small equal angles in opposite direc- 

 tions, from the position of crossed nicols, thus afford- 

 ing an accurate means of determining whether the 

 exact position of extinction of a mineral has been 

 arrived at. 



The "directions-image," showing interference 

 figures, is obtained, not by the insertion of a 

 " Bertrand " lens in the tube, but by placing a 

 " Becke " lens- over the ocular. This is decidedly pre- 

 ferable as it enables the optical effects of a small 

 crystal or twin lamella to be isolated by first placing 

 a diaphragm, with a hole of suitable dimensions, in 

 the focus of the ocular, so as to hide evervthing ex- 

 cept the object to be studied, and then putting the 

 Becke lens into position. The diaphrajgm is so 

 constructed that it allows of the insertion of 

 a gypsum plate or quartz wedge immediately 

 above it. 



These arrangements render it unnecessary to cut 

 into the tube of the microscope to allow of the intro- 

 duction of the analyser and the Bertrand lens. This 

 means less labour in construction, and therefore less 

 cost. 



It may be added that the upper lens of the ocular is 

 adjustable, so as to admit of its being exactly focussed 

 on the quartz wedge, the cross wires, or the perfora- 



tion in the diaphragm, and there is also an adjust- 

 ment of the Hecke lens for the purpose of focussing 

 the interference figures. 



The polariser is conveniently placed in a swing-out 

 below the stage. It has a slot immediately below it 

 for the insertion of a diaphragm with a small cir- 

 cular or linear aperture for comparing the refractive 

 indices of adjoining minerals by the Becke method, 

 and other purposes. 



When it is required to insert the condenser it is slid 

 up into a cylindrical fitting in the stage. This is not 

 very convenient, but we are informed that the firm is 

 arranging to substitute a swing-out attachment, which 

 it is believed will prove in every way satisfactory'. 



An interesting feature is the Sloan objective 

 changer, which takes only two or three seconds to 

 operate. Each objective is attached to a collar by 

 means of two screws. When these are once correctly 

 adjusted, the objective will always be found to be 

 correcllv centred immediately on insertion. 



Among the accessories is a quartz wedge cemented 

 to a gv|)sum plate, and graduated in intervals of fifty 

 microriiillimetres of relative retardation. This should 

 render unnecessary the quarter-wave mica and Klein's 

 plate, which are, however, still letained in the list 

 of accessories. 



It mav be suggested that the fine adjustment should 

 be provided with a milled head graduated to five 

 microns on its circumference, even if it were only 

 approximately accurate. 



Archaeology in Mexico. 



A T a meeting of the Royal Anthropological Insti- 

 -^*- tute on November 22 Mrs. Zelia Nuttall gave 

 an account of recent archaeological investigations in 

 Mexico. As an introduction to her report Mrs. Nuttall 

 referred briefly to the fact that after a period of 

 quiescence of some centuries the great volcano Popo- 

 catapetl had again become active in 1920, and that 

 its activity still continued. 



During the last decade evidence that great volcanic 

 disturbances had taken place at long intervals has 

 been forthcoming. Two distinct types of figurines 

 have been found in conditions which indicate 

 that the topography of the valley has been 

 changed and its inhabitants destroyed by great 

 catastrophes antedating the arrival of the Nahuas or 

 Aztecs. 



Of these figurines the first, provisionally distin- 

 guished as the sub-gravel type, was brought to Mrs. 

 Nuttall's notice in 1909, when specimens were 

 offered for sale by Indians, and she herself discovered 

 an example in sHu under a gravel bed at Atzaca- 

 potzalco. They were delicately fashioned of fine clay, 

 with slender bodies, long faces, smooth-hanging hair, 

 some wearing chaplets. All presented a worn and 

 polished surface. In the Valley of Mexico the gravel 

 beds extend under the lava flow at the base of the 

 extinct volcano Ajusco. 



llnder the lava bed, to which Dr. Tempest Ander- 

 son assigns an age of at least 20,000 years, Mrs. 

 Nuttall in 1908, and afterwards Senor Gamio, head 

 of the Department of .Archaeology of Mexico, have 

 discovered a second tvpe of figurine, to which the 

 name "sub-lava type" has been given. This type 

 is characterised by turbans and cans, evidentlv of 

 fine stuffs or fur, and decorated with circular orna- 

 ments of stone or sheU. They indicate that the 

 southern part of the valley was inhabited by a race 

 totallv distinct from that of the " sub-gravel type " 

 and the Aztec. The distribution of the clay figurines 

 NO. 2724, VOL. 109] 



is now under investigation. They have been traced 

 as far as Guatemala. 



Mrs. Nuttall also described the results of recent 

 excavations at Teotihuacan, during which a small 

 pyramid was opened up and reconstructed by Senor 

 Gamio. A tunnel pierced at the height of 35 ft. to 

 the centre of the pyramid revealed that it had been 

 formed of mud filled with innumerable fragments of 

 pottery vessels which had prevented the mud from 

 cracking when it baked in the sun. A remarkable 

 discovery was that of the remains of the ancient 

 pyramid teinple with a wonderful sculptured frieze 

 which had been partly destroyed and then concealed 

 bv another terraced pyramid temple built in front. 

 The sculptured serpents' heads and the masks of 

 the water-god Tlaloc are of a form hitherto unknown. 

 Associated with them are sculptured shells, principally 

 the conch shell and the pecten or pearl shell. Not 

 onlv is it remarkable that sea-shells should be repre- 

 sented in sculpture in the heart of the continent, 

 I but the association of the water-god with the ocean is 

 entirelv new. 



In the discussion which followed Mrs. Nuttall's 

 Daper, Mr. Maudslay expressed the hope that it might 

 be possible before long, by the elaboration of a system 

 of stratification, to date Mexican antiouities. As 

 Mexico appeared to have been untouched bv outside 

 influence, the study of its antiquities afforded evidence 

 of the highest value, for the studv of the development 

 of the human mind acting by itself. Mr. T. A. Jovce 

 emphasised the importance of the evidence relating 

 to the figurines, and pointed out that the British 

 Museum had acquired a fi£?urine of similar techniotie 

 from Ecuador. Prof. Elliot Smith expressed the 

 oninion that, dontrarv to what had been stated bv 

 Mr. Maudslav, Mexican antiquities showed clear evi- 

 (^'ence of influence from outside, and in particular 

 from .Asia. Mrs. Nuttall's work showed that this 

 culture must have crossed the Pacific. 



