authors. Its leading traits were: houses of coursed masonry, the rooms rectangular and arranged in series to form, when the site permitted, definite pueblos; subterranean ceremonial rooms or kivas; crania with strong occipital deformation and apparently originally brachycephalic; cultivation of several varieties of corn, as well as of cotton and beans; domestication of the turkey and use of its plumage for feather-string cloth; use of the bow and arrow; manufacture of great quantities of pottery of distinctive types, black-on-white, red-and-yellow, red, and corrugated.

The interrelation of the above three groups was not understood. The Basket-maker was obviously the earliest, the Slab-house next, and the Cliff-dweller-Pueblo latest; but whether they were to be regarded as stages in the development of a single people, or whether they represented successive occupations of the region by two or even three different tribes, could not be decided on the basis of the evidence available.

2. The explorations of 1920 in Sagi Canyon have added many new data. A few Basket-maker remains were found in various caves; these ran entirely true to the previously established type and, as usual, showed no admixture of later material (Slab-house or Cliff-dweller-Pueblo). Furthermore, a hitherto unrecognized culture came to light. At the west end of a large cave were unearthed rooms with slab foundations and stone and adobe superstructures; in and about the rooms was rubbish which yielded the following material: rough undecorated pottery of distinctive shapes, mostly black, some gray, a very little red, no trace of coiling; many sandals elaborately decorated in relief work and in colors, with a broad scallop across the toe end of each; handsomely ornamented woven carrying straps; crudely made twined bags. There was no cotton or turkey-feather cloth. In front of the cave lay a small burial mound containing skeletons with long, undeformed crania and accompanied by pottery identical with that from the rooms.

In the same cave, but farther to the east were discovered burials of the Slab-house culture; the identification was made by means of typical Slab-house vessels deposited with the bodies. The individuals had strongly deformed skulls. With them were: a large decorated carrying basket of a type not found with Basket-maker burials; cotton cloth; turkey-feather cloth; a complete bow and part of another; a twilled yucca ring-basket; a carrying strap of Cliff-dweller-Pueblo type; and a piece of rush matting. No house-structures associable with these graves were found, but the site was only partially excavated.

At the eastern end of the cave was a group of typically Cliff-dwellerPueblo rooms, containing an equally typical assortment of pottery, textiles, sandals and other objects of the Cliff-dweller-Pueblo period.

3. Present Status of the Investigation.-The Basket-maker culture is still to be considered the earliest in the region. A second culture, which we call the Post-Basket-maker, followed the Basket-maker. Its probable

1

descent from the Basket-maker is indicated by the dolicocephalic bead form and absence of cranial deformation; by the elaborateness of the sandal weaves; the presence of a degenerate type of twined-woven bag; and by the use of fur cloth instead of feather cloth. The absence of cotton from both cultures should be noted. Advances over the Basket-maker are seen in the appearance of pottery (albeit of a crude type), in the presence of permanent house-structures, and in the elaboration of the carrying straps.

The third culture is the one which we formerly called the Slab-house. As that term, based on a feature of the architecture, is equally applicable to the Post-Basket-maker we have discarded it and substitute the name Pre-Pueblo. This group is allied to the preceding one most closely apparently in house-types, and in the possession of pottery, though its characteristic wares are much the more highly developed of the two; it differs sharply from the Post-Basket-maker in the practice of skull deformation, in the possession of cotton, turkey-feather cloth and twilled basketry. Traits that it shares with the succeeding culture, the Cliffdweller-Pueblo, are: skull deformation; decorated pottery; cotton; turkeyfeather cloth; the bow.

From the above data it seems probable that the Basket-makers were the direct ancestors, both physically and culturally, of the Post-Basketmakers; the latter, however, had made considerable advances (houses, pottery). A direct line of descent from Post-Basket-maker to the PrePueblo might be inferred from the similarity in house-types; but the Pre-Pueblo are in most respects much more nearly allied to their successors, the Cliff-dweller-Pueblo people, than they are to the earlier group.

To sum up: Basket-maker is probably ancestral to Post-Basket-maker; Pre-Pueblo to Cliff-dweller-Pueblo; the genetic relationship of Post-Basketmaker to Pre-Pueblo may be inferred, but is still doubtful. A more detailed knowledge of the material cultures of the two middle groups is necessary, as well as studies to determine whether or not skull deformation alone is capable of producing the marked appearance of brachycephaly exhibited by the crania of the two later groups.

THE OPEN MERCURY MANOMETER READ BY DISPLACEMENT INTERFEROMETRY1

BY CARL BARUS

DEPARTMENT OF PHYSICS, BROWN UNIVERSITY

Communicated February 2, 1921

1. Apparatus.-This is practically a U-tube, AmA', figure 1, with wide shanks, AA', connected by a channel, m, below. A and A' are cylindrical hollows, 2-3 cm. deep and about 5 cm. in diameter, cut in a rectangular 1 Advance note from a report to the Carnegie Inst. of Washington, D. C.

block, BB', preferably of iron. The connection m must also be large in section, so as to admit of rapid flow from A to A'. The U-tube is charged with mercury MmM', M and M' being as shallow as possible to counteract the tendency to vibration. Thin plane parallel glass plates, gg', round discs of equal thickness and diameter, are floated on the mercury, which act as mirrors for the interferometer beams, L' and L", and also materially check the tendency of the pool of mercury to vibrate. It would be desirable to be able to use the mercury surfaces at M and M' directly without the intervention of the plate; but within the city limits the fringes are unsteady and hard to find.

The top of the iron block BB' is recessed as shown, to receive the plane parallel glass plates GG'. These like gg' must be equally thick; otherwise the fringes will be multiplied and faint. The annular space cccc between G and B is filled with resinous cement, poured in in the molten state. The air space AA' shut off in this way communicates with the atmosphere by two tubulures, t and t', in the front side.

The ray parallelogram of the quadratic interferometer of which L'L" are the interfering rays should be vertical. The displacements of the achromatic fringes of white light are read off by a telescope with an ocular micrometer (scale part 0.01 cm.). The fringes parallel to the divisions of the micrometer are conveniently made a scale part in size. The block BB' should be mounted separately from the interferometer. If it is placed on the base of the latter, all manipulations there shake the mercury in BB' and it is necessary to wait for subsidence. This, however, occurs very soon, so that the separate mounting is not absolutely necessary. Without manual interference the fringes are about as quiet as in a solid apparatus.

2. Experiments.-To test this apparatus the air space AA' was left with a plenum of air. With A' communicating with the atmosphere, A was joined through t and a filimentary capillary glass or metal tube, to an apparatus by which slight pressure could be applied. In the first trials I attempted to use a water manometer controlled by a micrometer screw; but the vibrations of the meniscus were at once impressed on MM' so that the fringes were hard to keep at rest. I then devised the apparatus shown in figure 2, which is merely an adaptation of the pin valve of an oxygen tank, with a good micrometer screw, s, and stuffing box, n. The

head h of the screw is graduated. The barrel b is at right angles to the tube aa', which at a joins the capillary tube d, leading to t of figure 1. At the end a' there is a cock, C, which shuts off communication with the atmosphere. Thus when C is closed pressure is applied directly at A, figure 1, by rotating the head h in figure 2. This pressure is at once removed by opening C.

The apparatus worked surprisingly well. When C is closed and h rotated, the fringes may be placed anywhere in the field about as conveniently as with the micrometer screw at the mirror of the interferometer. There is, however, one difficulty which I have not thus far been able to remove. When the pressure increments exceed a certain small value, the plates gg' no longer rise and fall in parallel. The coincidence of images is destroyed and the fringes vanish. There is here a conflict with the capillary forces present at the edges of the disc. I endeavored to improve this by using small plates gg', anchored near the centre of MM' by 4 loose threads. But the advantage was not marked. Fringes a scale part in size will not be available for more than 50 scale parts, being sharpest in the middle. This is about half the diameter of field of the ordinary telescope. Curiously enough, fringes from the free surfaces of mercury vanish in the same way, probably owing to surface viscosity of the mercury, not absolutely pure.

3. Equations and Pressure Observations.—If the cock C, figure 2, is closed and the temperature for brief intervals is considered constant, Boyle's law may be written (ignoring signs of increments)

where V is the total volume enclosed, do the increment at the micrometer screw hs, and dV the corresponding decrement equivalent to the pressure decrement dp. If a is the area of the piston at g dV = a dh/2 and if V = aH, H being the corrected air space at A, equation (1) becomes

But dh on the interferometer is equivalent to n fringes of wave-length so that dh nλ/2. Hence, finally

=

This equation gives a test of the trustworthiness of the gauge.

In the apparatus used the following constants were found by measurement: V = 66.8 cm.3, a 29.2 cm.2, H = 2.29 cm. The pitch of the screw was 0.073 cm. and its mean diameter 0.51 cm. Hence per turn

dv

=

0.073 X 0.204

=

0.0149 cm.3 and dr V

=

10-4 X 2.23 per turn. The mean wave-length being λ = 6 × 10−5 cm. equation 3 reduces to n = 3.2 fringes per turn of the screw hs.

In the experiments fringes of 1/2 scale part were installed. In separate experiments immediately after closing the cock C, a half turn of the screw produced a displacement of 8.3, 8.0, 8.0, 8.5, 8.5 scale parts, as the average, therefore 16.4 scale parts per turn or about 33 fringes per turn. This agrees as closely as may be expected with the number computed.

=

The pressure increment per turn of screw is dp n/2 cm. of mercury or per turn of screw about 10-3 cm. Per fringe, therefore, 3 X 10-5 cm. of mercury as anticipated. A range of about 2 or 3 turns of screw was possible with each fringe, i. e., the range of pressure measurement should be from 3 X 10-5 to 3 X 10-3 cm. of mercury.

Experiments of the same kind were made in great variety. There is no difficulty in using much larger fringes so that 3 X 10-6 cm. of mercury should be appreciable. By exhausting both sides of the U-tube the apparatus becomes a vacuum gauge. I did not, however, attempt much work with it as the present apparatus was not well adapted for the purpose. Air Thermometer.-If the cock C is permanently closed, the air space A becomes the bulb of an air thermometer of approximately constant volume. In this way the heat produced by the rays of light L' may be measured. In a variety of experiments of the kind, the mean result was about 10 scale parts or 20 fringes in a lapse of 210 seconds. If r denotes absolute temperature, the intrinsic equation may now be written

T

or the heating produced was 2 X 10-4° C. per second. Whether, supposing AA' to be filled with water, a pyrheliometer may be constructed on this principle I have yet to learn.

Other interesting results of the same kind might be mentioned. Thus if the screw stopcock, figure 2, is closed quickly (C being open) there is always a decided increment of pressure. In other words in consequence of the viscosity of air, the fine space at the plug is virtually a closure before the screw is checked by an actual closure.

If the glass plates G are removed and the air space A is closed by a pipe, P, tapering to a neck as in figure 3, it becomes a closed organ pipe adapted for the measurement of acoustic pressure. It may be blown by an adjustable embouchure, j, described heretofore (Science, 53, 1921 (47)), or