field we have, however, like other investigators, been compelled to begin with merely local problems; but the solution of these local problems has—so we believe-led to the discovery of simple methods applicable to the Pueblo problem in its entirety.

The Field Data.-The Pueblo Indians, in the light of the ethnological and historical information we have concerning them, may be defined as a group of sedentary tribes who build substantial rectangular houses of a more or less compact and communistic type, who commonly construct semi-subterranean ceremonial chambers, either round or rectangular, who build reservoirs and irrigation ditches, who grow corn, beans, and squashes for food as well as cotton for clothing, who grind their corn on a metate, who use the curved rabbit-stick and the tubular pipe, who possess a special type (or types) of grooved ax, who work turquoise and who make pottery having very striking local peculiarities. The ethnologist would indicate additional characteristics of a linguistic, social, and religious nature; but these because they have received less definite or permanent material expression are of secondary importance to the arachaeologist as working data. Some of the cited traits, like maize growing, the Pueblo share in common with other and even very distant tribes of North and South America; certain other traits like the round ceremonial chamber are only partially diffused over their own territory; and still other traits, like cotton growing and the stone ax, have completely disappeared in modern times. Perhaps the most characteristic of the surviving traits, considered both as geographical and as historical phenomena, are architecture and ceramics.

The tribes who today exhibit the above characters are domiciled in about thirty villages specifically known as pueblos in contradistinction, first, to the less local, rather loosely constructed and only semi-permanent type of villages known as rancherias and, second, to the still more widespread temporary settlements known as camps. Their numerical strength, according to the last census is about 11,000 souls; and their territorial possessions, in the form of land grants and reservations, are officially placed at about 5,000 square miles. These artificial boundaries are not exactly conterminous with the actual range of the tribes but the figures give a fair idea of the amount of territory from which they draw sustenance.

In 1540 or thereabouts when the Spanish explorers first entered the country the Pueblo appear to have inhabited all of seventy villages and to have numbered about 20,000, a few more or less. Their territorial range was about 13,000 square miles, or more than twice what it is today, a large section having been vacated, e.g., on the southeast. That much is determined for us in part by the historian; but from this point on for another short stretch only the ethnologist can accompany us.

After several decades of more or less desultory work we are now in position to say that the Pueblo in prehistoric times ranged over a territory little short of 140,000 square miles in extent, throughout which they have left ruins and other characteristic remains very similar to those found in the territory still

occupied. Beyond this territory, finally, there is a wide marginal zone, which taken together with the central area is little short of 1,000,000 square miles in extent, and throughout which appear ruins and remains in some respects like those of the Pueblo area proper and in other respects like the remains characteristic of Nomadic regions, i.e., essentially 'rancherias.' In short, the geographic distribution of Pueblo traits takes the form of a center of high and unalloyed development and a marginal zone different segments of which have been more or less affected by influences from other adjacent culture centers. The bearers of the pure Pueblo culture still reside in the heart of the old center; and several tribal groups of the hybrid Pueblo-Nomad type also continue to reside in the western and southern portions of the marginal zone. Lastly, several slightly modified but vigorous strains of nomadic cultures are present on the north and southeast, not only in the marginal zone but in considerable stretches of what was once pure Pueblo domain. The spatial condition of affairs is diagrammatically represented in figure 1.

On the face of it the diagram indicates two things: first, a tremendous geographical concentration of the pure Pueblo culture or as we might just as well say, a falling off in Pueblo influence; and, second, and what amounts to the same thing, several great nomadic invasions which have swallowed up or pressed back the Pueblo traits on the north and southeast and all but detached several small marginal centers on the south and west. After several years of contact with the facts of this situation the writer is unable to escape the conclusion that they are all very intimately connected and that either set of them largely explains the other. At this point, then, we have to leave the ethnologist behind: if we wish to know anything further we have to dig below the surface. Given the spatial phenomenon presented in our diagram, it is for the archaeologist to present the same set of facts as a time phenomenon, in other words, to arrange the data in their proper historical sequence. And to do this he must devise adequate methods of his own.

Concerning Methods.-One of the difficulties that the archaeologist has labored under has been the mass of the data confronting him. In his effort to master details he has lost touch with the problem as a whole. No one man has yet seen the entire field with his own eyes. Dr. J. W. Fewkes, who may be said to have initiated the last phase of the investigation, has, e.g., done his work largely in the western sector and has generalized on the problem from that point of view, using mainly architectural traits as a basis. Dr. A. V. Kidder has worked mostly in the northern sector and has generalized mainly on the basis of ceramic traits. Both employed the method of direct comparison. The writer finally has done his work chiefly in the southeastern sector, using ceramics as a medium and employing as a method, in addition to that of direct comparison, the simple principle of stratification. Resort to this medium and to this principle came about in a very natural manner.

The data we have to deal with consist of some six or seven hundred major, i.e., pueblo, ruins of various types, located within our center of high develop

ment; and, in addition, an untold number of minor ruins, partly of the rancheria type, scattered over both the Central area and the great Marginal zone. The immediate problem confronting the archaeologist has been to decide whether these ruins were chronologically separable. Until recently the general verdict has been that they were not, except of course within the narrow limits of 'historic' and 'prehistoric.' A third and intermediary group we may perhaps concede to have been detached on the basis of traditional references to it, but that is all. Our prehistoric ruins were simply 'prehistoric,' that is, roughly speaking, they were of the same age: and the result has been some extraordinary speculations about great numbers of peoples and their mysterious disappearance, which has finally been credited by some to a fancied 'change of climate.' Unfortunately, the appearance of the ruins was no criterion of age. Neither did the achitecture as architecture give away in a really clear manner the order of development, doubtless partly because architecture is in a large measure determined by environmental conditions. Pottery-an ever present accompaniment of the ruins-is on the other hand, an exceedingly plastic phenomenon, varying from place to place and from time to time, in response to the inventive faculty, far more readily than does architecture. We may therefore decide the relative age of any given ruin by determining the age of the particular style of pottery which it exhibits; and this latter feat is easily accomplished. We have but to find the stratigraphic position of this particular style in the total series of styles as they occur in refuse heaps or in actually superposed ruins. Sometimes the stratigraphic position has to be determined without digging into the refuse heaps-there being none, but the principle involved is the same: we have to begin with the style of ware lying on top or still in use and must work back or down through the series until we arrive at the bottommost style, which is the oldest. We may indicate our general procedure therefore by saying that instead of as formerly hunting out the most picturesque ruins for excavation or at any rate the ruins giving promise of the finest outlay of specimens, we have begun commonly with the despised ruins of historic date situated in the heart of the present Pueblo habitat.

Results to Date.-Our method has not yet been applied to the entire Pueblo area and consequently our results are not complete in respect to numerous details. Nevertheless, the general outline of things, i.e., the chronological disposition of the ruins, is already tolerably clear and has been diagrammatically represented in figure 2 which is, as it were, a section in the A-B line of figure 1. To date we have, so to speak, dug down through the superposed culture levels found in both the Zuni and the Tewa circles, in fact through several additional but more ancient circles not presented in the diagram. By thus discovering the time order of things we have with the same effort discovered the key to the whole spatial arrangement. For as we dig down through the vertical series we pass gradually from Pueblo to Rancheria traits and from Rancheria to Nomadic traits exactly as if we were traveling from the present center of Pueblo life out over the various zones to the Nomadic border. Briefly, it is archaeolog

FIG. 2. TIME DISTRIBUTION OF PUEBLO TRAIT GROUPS, IN A-B LINE OF FIGURE 1

ically demonstrable, as perhaps many will say they knew long ago, that the Pueblo culture grew out of a Nomadic one.

Conclusions.-There is no space here for the discussion of details. There remains to add however that it is not clear whether the Pueblo phenomenon is something altogether special in culture or whether in reality it is a fine illustra

tion of a general principle. That is, I am not certain whether the accident of Nomadic invasion produced the outstanding Pueblo traits or whether in the absence of such pressure we should have observed the same phenomenon in all its essentials. In short, does or does not the 'age and area' hypothesis, commonly subscribed to by students of organic life, hold true also in the province of human culture? But, passing over that detail, one thing seems fairly established both here in the Southwest and in several of our eastern culture areas. It is that North America north of Mexico, before it became settled by sedentary agricultural tribes who developed many of the traits common to that type of life the world over, was settled by a generally more primitive nomadic type of peoples subsisting mainly by hunting, such as still persist over all of the northern and northwestern portions of the continent. The above summary account is based upon data from the Archer M. Huntington Survey of Southwestern United States conducted by the American Museum of Natural History. The full report upon this survey will be published by the Museum.

AN ADJUSTMENT IN RELATION TO THE FRESNEL COEFFICIENT1 BY CARL BARUS

DEPARTMENT OF PHYSICS, BROWN UNIVERSITY

Communicated, February 10, 1919

1. Apparatus. One internal reflection. The specific part of the apparatus is the glass cylinder, G, figure 1, with a carefully polished mantel, capable of rotating around an axis, A, normal to the ray-plane of the interferometer.

If micrometer facilities are to be dispensed with, and that is permissible in the present experiment, the interferometer may be designed as in figure 1. The white light L from the collimator takes the respective paths dCC'd'b and bd'C'Cd, the plate N being half silvered and N' an opaque mirror. The telescope or spectro-telescope is at T. The glass face at N may be turned either way.

Such an interferometer is self adjusting (cf. preceding paper). In the form, figure 1, two reversed spectra will be visible in the telescope, which if superimposed by rotating N or N' on a vertical axis, will show the linear phenomenon at once, in any color at pleasure. The fringes may be enlarged by rotating N or N' on a horizontal axis and they are symmetrically equal in size on the two sides of the adjustment for infinitely large fringes.

If the achromatics are wanted, a prism must be inserted into the rays b (preferably) between N and N', with a prism angle and other conditions selected to counteract the refraction of the cylinder G.

2. Apparatus. Two internal reflections. As the fringes were found without much difficulty (§5) in case of one internal reflection, it seemed desirable