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TABLE 1NICKEL-NICKEL NEIGHBORS AND FOREIGN ATOM-NICKEL NEIGHBORS

C(2 X 2) P(1 X 2) P(2 X 1) P( X 1)Carbon-nickel Oxygen-nickel Hydrogen-nickel Clean

surface surface surface (surface(Fig. 2A) (Fig. 2B) (Fig. 2C) Fig. 2D)

M 7 7 6 6N 31/2 31/2 21/2 0

Difference 3'/2 31/2 3'/2 6

On the other hand, the situation is different for adsorption of oxygen or carbon.For these atoms, the bond between nickel and the foreign atom is known to bestronger than the nickel-nickel bond, and a dominant factor determining the sur-face structure may be the tendency to make the number of these heterogeneousbonds a maximum. The stable structures for oxygen and carbon are completelydifferent, but they have in common a decrease in the number of nickel-nickel bondsper unit area, this decrease being exactly the same for the two structures. Foreach structure, the number of missing nickel-nickel nearest-neighbor bonds per cm2is greater than in the hydrogen structure by 21/2/a02. At the same time, the numberof nickel-foreign atom neighbors per cm2 is greater than in the hydrogen structureby this same number. Since the heterogeneous bond is stronger than the nickel-nickel bond, one might expect that both the C(2 X 2) structure and the ['(1 X 2)structure would be more stable for carbon and oxygen than the P(2 X 1) structure.This is found to be true. More refined analysis will be required to determine whycarbon produces the C(2 X 2) structure and oxygen the P(1 X 2) structure.

* Present address: Cornell University, Ithaca, New York.1 Germer, L. H., and C. D. Hartman, Rev. Sci. Instr., 31, 784 (1960).2 Germer, L. H., E. F. Scheibner, and C. D. Hartman, Phil. Mag, 5, 222 (1960).3 Germer, L. H., and C. D. Hartman, J. Appl. Phys., 31, 2085 (1960).4Germer, L. H., and A. U. MacRae, J. Chem. Phys., in press.' For further observations regarding oxygen adsorption, see Germer, L. H., and A. U. MacRae,

J. Appl. Phys., in press. This paper contains descriptions of cleaning procedures. Also, Germer,L. H., and A. U. MacRae, Robert A. Welch Foundation Research Bulletin No. 11, November1961.

6 Wortman, R., R. Gomer, and R. Lundy, J. Chem. Phys. 27, 1099 (1957).7 Beeck, O., W. A. Cole, and A. Wheeler, Discussions Faraday Soc., 8, 314 (1950).8 Further observations regarding hydrogen adsorption are contained in a paper by L. H. Germer

and A. U. MacRae, J. Chem. Phys., in press.

COLORS SEEN IN A FLASH OF LIGHT

BY EDWIN H. LAND AND NIGEL W. DAW

POLAROID CORPORATION, CAMBRIDGE, MASSACHUSETTS

Communicated April 30, 1962

Color is not a time-dependent phenomenon in common experience. A coloredsweater does not change its- color as one looks at it. Its color does not depend onwhether one has been looking at a red, green, blue, or gray object immediately be-fore, nor does it change significantly as one walks from a room lit by tungsten light

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into a room lit by fluorescent light. These phenomena are wvell documented in theliterature on color vision.1

Colors seen in a flash of light appear much the same as they do in continuousillumination. Thus Smith, on showing his children how short a flash of lightningis by rotating a color top in its light, noted that the bands of color stood out clearly.2Young used a spark from a Leyden jar to illuminate a room and described everythingas perfectly visible:' he did not mention color, and if there was anything strangeabout it, he must have considered that it was not worth mentioning. Rood, alsoworking with a Leyden jar, noticed that Loewe's rings can be seen in a flash.4More recently, Rouse, in working on the Bunsen-Roscoe law for different wave-lengths, found that the color reports did not vary with the duration of the stimulus,provided the quantity of light was above threshold.' This last experiment, how-ever, was done with a spot of light and a limited variety of wavelengths, and oneshould be careful in applying its results to more complex situations.

In this paper, we consider the gamut of colors seen in the projection of a pairof images in red light and white light.6 We ask whether these colors, which includeblue, green, gray, brown, black, orange, yellow, and pink are the same in a flashof light as in continuous projection. Some preliminary experiments performed witha camera shutter held before the eye indicated that this is so.7 The following ex-periments examine the question in more detail and under more rigorous conditions.

First Experiment.-The first experiment was performed with the dual projectordescribed previously.6 The tungsten bulb was replaced with a General ElectricFlashtube type FT217, activated by a modified General Radio Strobolume type1532A. The system was designed by Harold E. Edgerton and John Tredwell ofM. I. T. to give more output than usual from this type of flashtube, and the dura-tion of the flash was measured as 25 microseconds from 1/3 peak value to 1/3 peakvalues, 60 microseconds from initiation to 1 per cent peak value.Two black and white photographs were made of a scene, one through a Wratten

#24 filter passing wavelengths between 580 and 700 mAt in the long wavelength re-gion of the spectrum, and one through a Wratten #58 filter passing wavelengthsbetween 480 and 600 mA in the short wavelength region of the spectrum. We shallrefer to such a pair of photographs, for the sake of convenience, as the long recordof the scene and the short record of the scene. These two records were thenmounted in the projector, and their images were registered on the screen. A Wrat-ten #26 red filter was placed over the lens projecting one record, and a neutral den-sity of about 1.1 over the lens projecting the other record. The picture used was ofa flag. It was shown first with a red filter over the short record and a neutraldensity filter over the long record. This reverses the colors when such a pair ofrecords is viewed in continuous illumination, that is, objects which are ordinarilywarm look cool, and vice versa.The experiment was usually performed with an audience or observers who had

been sitting in a dimly lit room for several minutes. A little light was left on in theback of the room during the experiment. This was just enough so that peoplecould tell where the screen was. They were asked to look at the center of the screenand the projectionist would say, "one, two, three, flash," pressing the button of theStrobolume on saying "flash." The observers were then asked what they saw, andwhat color the stripes were. After this response had been noted, the Strobolume

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was flashed a second time for another response, then several more times to satisfythe curiosity of the observers.The filters over the lenses of the projectors were then interchanged, so that the

red filter was placed over the lens projecting the short record. This is a combinationwith which objects have colors close to their ordinary ones. As before, the Strobo-lume was flashed once, and the audience was asked what they saw. Then it wasflashed again for a second response, and several more times after that.

This experiment has been shown many times. It has been shown on eight oc-casions to large audiences, and on many other occasions to groups of observers andto individual observers. In each case, the observers were asked to give their re-sponse out loud. First they would be asked what color they saw to crystallize theiropinion. Then, for example, depending on the object, those who saw blue would beasked to say "blue," those who saw green to say "green," and those who saw gray tosay "gray." It was impossible in these conditions to keep exact statistics, but itwas easy to keep track of situations in which only three or four out of a hundredresponded differently from the group as a whole.Most observers identified the flag in the first flash. Their response to the ques-

tion, "what do you see?" was "flag." When asked "what kind of flag?" they wouldsay unhesitatingly, "American flag," in spite of the strange color. This responsedid not depend on the angular subtend of the image, and the flag was identifiedimmediately when only a small fraction of its image covered the fovea.The response to "what color are the stripes?" was preponderantly "green," oc-

casionally "blue," and infrequently "gray" or "black." Some people would say"green and white" rather than "green," but it was obvious in each case what theywere referring to.A few observers saw nothing in the first flash. These were people who had been

blinking, or were looking in the wrong direction. Nearly all of these observers sawthe second flash, and reported then in much the same way as the other observershad for the first flash. Each succeeding flash added certainty to the over-all re-sult that the stripes were a cool color and that the whole flag could be identified inone flash.When the filters were changed so that the red filter covered the long record and

the neutral density the short, the flag appeared in its correct colors with the skyrecorded as bluish rather than pinkish. This also was observed in the first flash,and subsequent flashes did not affect the over-all impression.

Second Experiment.-The first experiment showed quite convincingly that somecolors seen in a "red and white" projection, such as green and blue, which one doesnot traditionally expect to see, are observed in a flash of light. Thus, these colorsare shown not to be the result of alteration in some relatively slowly changingmechanism of the eye. Unfortunately, the method did not allow us directly to makea comparison of colors seen in a flash of light with those seen in continuous illumina-tion, because the flash was a xenon source and the continuous illumination tungsten.In the second experiment, we devised a procedure for making this direct comparisonand for taking statistics on the results.The photographs for the second experiment were 8 X 10 in. transparencies taken

in the same manner as in the first experiment, mounted at right angles to each otherand superimposed by a semisilvered mirror. Figure 1 shows a schematic diagram of

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J AROBOTACS

LONG RECORD

0

U

4~~~0I

OBSERVER

FIG. 1. FIG. 2.

the apparatus, without the baffles and vertical staggering of some of the compo-nents. Illumination was provided by two General Radio Strobotacs (Type 1531lA),connected together to flash in unison. They could emit a pulse lasting six micro-seconds or be run on line frequency to give effectively continuous illumination.They were placed so as to illuminate white matte surfaces behind the transparencies,which gave fairly even illumination.' Only one set of transparencies was used inthis experiment; the short record is shown in Figure 2.The observer was first shown an outline of the objects in the picture, with num-

bers attached to each object, so that he could identify the objects when describingthe colors. Next, he was handed the button which activated the Strobotacs, andasked to press it once. A piece of black paper was placed in front of the long record,so that only the short record in black and white was seen. This enabled him toget used to the apparatus and see what a microsecond flash was like. We found itnecessary to ask the observer to press the button himself, so that he could coordinatehis attention with the flash, and would not fail to see it because of a blink or an eyemovement.The piece of black paper in front of the long record was removed. The observer

was asked to flash the strobe light just once, and to describe everything that he saw.He was then asked to flash again, pressing the button regularly but slowly, until hecould describe the color of object 1, and to pass on to object 2, and so on, until allten objects were described. The number of flashes required to describe all ten ob-jects was generally between nine and eighteen. The room lights were kept on ata level sufficient to inhibit after-images, but not too great to wash out the colors inthe primary impression.

Next, the light was put, on line frequency, which provided effectively continuousillumination of the same spectral composition as the pulse. The observer wasasked to report, the colors which he saw in the first few seconds. After this, hewas made to continue looking at the picture for another five minutes or longer byconversation with the experimenter. They would discuss the objects in the picture

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so that the observer's attention was always on the picture. At the end of thisperiod, the observer was asked again to describe the colors which he saw.There were ten observers, none of whom had seen the picture before, and six of

whom knew nothing about color vision work in this laboratory. It is interestingto note that most of them recognized the decanter in the first flash, and some sawthe goblet. Very few saw anything else, and if they did they were unable to de-scribe it.The results were tabulated in terms of the number of observations which gave the

same color in a flash and in continuous illumination, the number which gave dif-ferent results, and the number which gave questionable results. Examples of ob-servations which were regarded as the same as each other are orange-red and red,olive green and green, moss green and mint green, cream ivory and dull white,pinkish gold and pink, flame color and red, lime and light green, dull silver andwhite, light golden and amber, maroon and dark red, and maroon with violet andpurple; examples of observations which were regarded as different are white andyellow, yellow and pink, green and blue, green and aqua, blue and black, pink andorange, violet and blae, purple and brown, purple and gray, gray and green, yellowand orange, orange and red, tan and gray, pink and white, red and tangerine, blackand dark green, and red and brown; examples of observations which were regardedas questionable are yellow and beige white, yellow and yellow orange, white andgray, plum and dark brown, light orange and pink, gold and silver, tangerine andreddest of all, orange and light brown, golden and orange, black and gray.Out of 100 observations in this experiment, 73 were the same, 18 were different,

and 9 were questionable in the comparison of observations made in a flash and incontinuous projection in the first few seconds. No one saw any change between thefirst few seconds of continuous projection and five minutes later.

Third Experiment.-In the two experiments described above, several objectswere such that their colors had some association with the shape and texture of theobject, e.g., the lemon. In this experiment, most of the objects were chosen becausethey had no such association. It was performed with a pair of prints taken in thesame manner as the transparencies for the first experiment. The pair of prints wasexposed in a beam-splitting camera and superimposed for viewing by another beamsplitter similar to the one used in the camera (see Fig. 3). The illumination was

LONG SNORTRECORD RECORD

L 2 = ARED NEUTRAL |FILTER FILTER

STROBOTAC STROBOTAC

SEAM SPLITTER

FIG. 3. FIG. 4.

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the same two Strobotacs as those used in the second experiment, placed to the sideof the pictures. A board around the beam splitter prevented the light from reach-ing the observer's eye directly, and a rubber cup kept his eye in the correct place forviewing.We used six pairs of pictures of the scenes shown in Figures 4-8. Three of these

consisted of objects placed on a gray board divided into squares and numbered sothat the objects could easily be identified. The other three pictures were of a doll(Fig. 7), of oranges painted different colors (Fig. 8), and of familiar objects. Thelast was used to show the observers how the machine and flash mechanismworked.

F 5 F 6

FIG. 5. FIG. 6.

The observer was first shown this last picture in continuous illumination so thathe could see how his eye should rest in the eyepiece. He was told that the objectof the experiment was to see if the colors seen in a flash were the same as those seenin continuous illumination, and we tried to make it clear to him that this was a testof color vision theory and not of himself. Then the machine was turned to flashillumination and he was shown how this worked. He was to press the button slowlyand deliberately with a pause between each flash. With each picture, he was askedto press the button once and describe everything which he saw in the first flash.Then he was asked to start with object number 1, flash slowly until he could describeits color, then pass on to object number 2, and so on until he had described all theobjects. The average was about three~flashes for each observer for each object.Then the machine was turned to continuous illumination, and the observer wasasked to report again the colors which he saw.

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TABLE 1Number of observers who saw a

different color in a flash from that Description ofObject* seen in continuous illumination object Colors seen4.3 0 Yarn Red4.12 0 Glove Black5.2 0 Doll Red5.4 0 Can Black5.8 top 0 Block Red5.12 0 Napkin Orange, red6.5 0 Cup Pink, orange6.8 0 Telephone Red4.1 1 Cup Red-brown4.9 1 Bowl Orange-red5.11 1 Teapot Gold6.6 1 Plate Black or blue6.9 1 Saucer Brown6.12 1 Orange Orange4.8 2 Yarn Blue or green or black4.11 2 Cup Brown5.7 2 Cup Blue or green5.8 bottom 2 Block Black or blue5.9 2 Saucer Brown6.1 2 Teapot Green or blue6.2 2 Cup White or gray6.11 2 Inkstand Black4.4 3 Movie reel Gray4.7 3 Jug Green or blue5.1 3 Cat Gray or pale brown5.8 middle 3 Block White or yellow6.4 3 Stapler Gray4.2 4 Measure Off white4.5 4 Measure Green or blue4.6 4 Cup Pink or orange4.10 4 Yarn Black or green5.3 4 Cup Green or blue5.5 5 Pot ?5.6 5 Cup Yellow or orange or pink5.10 5 Dog Gray or green or brown6.3 5 Lemon Yellow or orange6.7 5 Plate Green or blue

* 5.4 refers to the object in square 4 in Fig. 5.

Eight observers looked at the slides, none of them being those who observed theprevious experiment. Some were young and some old; five were women and threewere men. One had strong astigmatism, but this did not make her results sig-nificantly different from those of other observers. One was very nervous and wasasked to repeat the first set of observations which she made. One, in spite of whathe was told, seemed to think that the experiment was a test of himself; we distrustedhis results and discarded them. On the whole, the observers were at ease, althoughthe surroundings and circumstances of the experiment were quite foreign to them,and they gave honest and direct answers.

For the objects on the board, 178 (67%) of the colors seen in a flash were the sameas those seen in continuous illumination; 65 (24%) were different; and 23 (9%)were questionable. For the oranges, 51 (60%) were the same; 30 (35%) weredifferent, and 4 (5%) were questionable. The number of observations which werethe same in a flash and in continuous illumination was remarkably constant for thevarious observers, being 74, 70, 60, 62, 68, and 66%.

Other noticeable points were:

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(a) We got the feeling that there might have been some association in the de-termination of object #8 in Figure 5. This consisted of three blocks on top of eachother-one red, one white, and one blue.

(b) Object #10 in Figure 4 was always seen as black in a flash and green or bluein continuous illumination.

(c) Two people said, looking at object #3 in Figure 6, "It is an orange, but itlooks yellow."The picture of the doll sitting beside leaves (Fig. 7) was put in to find out if the

leaves wc:e a cool color all e-er. The significant point about this picture is thatthe leaves in the top left-hand corner are surrounded by black. The nearest redportion of the picture is some distance away. Nevertheless, the leaves were onecolor all over when viewed in a flash, and this color was the same cool color as thatseen in continuous illumination in approximately the same proportion of cases asthat recorded for other pictures.Discussion.-We noted for each object the number of observers who saw a color

in a flash which was different from that seen in continuous illumination, to find outif there was any correlation between the color and type of object and whether thesensation was the same or not. The following table gives these results for Figures4-6. Results from the other slides were not well enough documented to be in-cluded in these tables.

In the column describing the colors seen, all the principal observations are in-cluded. The purpose of the experiment was to find out if these colors were the sameor different in a flash and in continuous projection. The. actual colors concernedare, of course, irrelevant to this question. Some observers were tested for colorblindness, wherever such a defect was suspected, but none was found. If one ofthe observers had been color blind, his results would have been as valid as those ofanybody else.The colors seen in a flash embrace the same gamut of hues as those seen in con-

tinuous illumination. In so far as there are uncertainties when observing in a flash,the uncertainties are not preferential for any hue. There is no systematic trend,such as green objects always being identified as blue, or vice versa. Familiarobjects, such as the lemon, do not appear to be identified more readily than otherobjects.The one noticeable correlation is a certainty, rather than an uncertainty. Red

objects are always identified as red, in a flash, and no observer changes his opinionwhen the light is turned on continuously.8 This suggests that the uncertainties aredue simply to lack of information. Red objects are the one class of objects wherethe information content is sufficiently high that they can always be identified. Themistakes made in the identification of other objects, being due to lack of information,were of a random nature.

In summary, we may say that the field phenomena which, in our opinion, produceand determine color are activated instantaneously and do not depend on fatigueand adaption.9 The mechanism which produces the greens, blues, browns, blacks,grays, and oranges in a picture projected with only red and white stimulation isready, waiting to act immediately after it is stimulated. It does not depend onsome previous stimulation to change its state before it can operate to produce allthis. It does not adapt; it simply acts.

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1 For a list of references see Edwin G. Boring, Sensation and Perception in the History of Experi-mental Psychology (New York: 1). Appleton-Century Company, Inc., 1942) and Committee onColorimetry, Optical Society of America, The Science of Color (New York: Thomas Y. Crowell,1953).

2 Smith, B. W., Nature, 6, 242 (1872).3Young, C. A., Amer. J. Sci., 103, 262-4 (1872).4Rood, 0. N., Amer. J. Sci., 102, 159-160 (1871).5 Rouse, Richard O., J. Opt. Soc. Amer., 42, 626-630 (1952).6 Land, Edwin H., these PROCEEDINGS, 45, 115-129 and 636-644 (1959).7Land, Edwin H., J. Opt. Soc. Amer., 50, 268 (1960).8 It is interesting to note in this connection that Rouse's observers confused green with blue,

during their training period, much more often than any other pair of stimuli.9 The word adaptation is used in this paper to signify a change of state in a biological mech-

anism, which alters the operation or sensitivity of the mechanism to meet different circumstances.Some authors recently have used the word in a sense which may turn out to be broader than thiswhen we find out how the mechanisms which they are considering operate, e.g., Schouten andOrnstein, J. Opt. Soc. Amer., 29, 168-182 (1939).

THE AFFINITY OF NARCOTIC AGENTS FOR INTERFACIALFILMS*

BY JOHN A. CLEMENTS AND KENNETH M. WILSON

THE CARDIOVASCULAR RESEARCH INSTITUTE, UNIVERSITY OF CALIFORNIA SCHOOL OF MEDICINE,SAN FRANCISCO, AND THE DEPARTMENT OF ANESTHESIOLOGY, THE JOHNS HOPKINS MEDICAL SCHOOL,

BALTIMORE

Communicated by Julius H. Comroe, Jr., April 12, 1962

Although investigators have suggested for many years that inert gases cause nar-cosis by acting on the lipid-containing membranes of excitable cells, a direct demon-stration of this localization has not been forthcoming. In contrast, Pauling1has recently suggested that inert gases induce narcosis by seeding aqueous clathratemicrocrystals in cells, which impede the ion movements that are thought usually toaccompany excitation. In support of this idea he has shown that the anestheticpotency of inert gases is systematically related to the stability of their clathratesand to the electronic polarizability of their molecules or atoms. He refers to thecellular lipids as insulators and suggests that they are not primarily involved innarcosis. Miller2 has also recently suggested that inert gases produce narcosis byforming hydrates not necessarily in strictly stoichiometric proportions, i.e.; "ice-bergs," with the water in or around excitable cells. Both authors mention the in-stability of such complexes at 370C and invoke the cooperation of materials intrinsicto the organism to explain structuring of water to a significantly increased degreeat partial pressures of inert gases which actually cause narcosis. Miller suggeststhat "iceberg" formation may occur particularly at interfaces and alter the phys-ical state of membranes, decreasing their electrical and chemical reactivity.For example, if it is assumed that a free energy of activation determines penetra-tion through a nerve membrane and contiguous material and thus regulates ex-citability,3 then the action of the narcotic might be described as increasing this

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