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As on the preceding morning, the moonlight was very bright. In the earlier part of the watch there was an aurora, with streamers reaching up half or two-thirds of the way to Polaris.
We called those meteors conformable which moved in paths which if produced backward would cut the curve of the sickle in Leo. But in the practical application of this criterion to tracks distant from the radiant it is probable that any which would strike within 10° of the center of the sickle were called conformable.
Of the apparently conformable meteors, some were undoubtedly accidentally so. The earth's motion being so nearly toward the radiant, a special tendency toward conformability in the sporadic meteors was the result. If we take 15 per cent of the 74 unconformable meteors away from the 79 conformable ones, and add it to the 74, it would be, I think, a tolerable correction for the accidental conformability. The numbers would then stand 85 unconformable meteors, and 68 November meteors, or Leonids as they have been called.
The only meteor seen by me near the sickle would correspond to a radiant one-third or one-fourth of the way from gamma to epsilon Leonis. It was moving at a large angle with the line joining those stars.
Many of the conformable meteors had the peculiar light and train which belong to the Leonids.
On the morning of the 15th the sky was overcast at New Haven. Between eleven and twelve o'clock P. M. of the 14th, however, there were a few breaks in the clouds. I think there could not have been any great number of meteors at that time, as I did not see a single one through the openings.
2. At Brunswick, Me.—The following is from a letter of Prof. Rockwood of Bowdoin College.
"I was abroad from Oh 45m till nearly 5h A. M., Nov. 14th, and assisted by two members of the senior class of Bowdoin College, kept a watch and count as given below. The time is local time, as nearly as could be ascertained.
66 2h 45m
16 “We saw 10 or 12 more, mostly conformable, at times when not engaged in the formal count. The sky was mostly clear, but sometimes partly obscured by a few light passing clouds.
“The number of meteors was not large but sufficient to prove the return of the November shower. Especially noticeable
4 20 25 17
8 24 29 21
facts were—(1) the almost perfect conformity to the radiant of brighter meteors ; (2) the uniformity in the number of the unconformable meteors.
On the morning of Nov. 15th, 1870, it was cloudy and raining."
Upon the chart sent by Prof. Rockwood are six tracks of meteors observed by himself. The following are their apparent places of beginning and ending. Time. Beginning.
1501 -145 The fourth of these paths was close to the radiant and would, if carried back, cut the line joining y and e Leonis three-sevenths of the way
from gammal. 3. At Burlington, New Jersey, November 14, 1870.—Mr. B. V. Marsh observed meteors as follows: from Oh 30m A. M. to Oh 45m A. M., looking south from a window, 3 conformable. In the open air, attention directed principally toward the south, sky perfectly clear:
13 Towards 3 o'clock clouds began to interfere materially, and at daylight the whole sky was covered. About half the number were equal to stars of 1st magnitude and several had trains, but there was no one that was worthy of special remark.
Mr. John G. Gummere from 11 to 3 o'clock, saw 9 conformable and 2 non-conformable; total 11.
Prof. Kirkwood reports a cloudy sky at Burlington, Ind.
Probably Prof. Rockwood and Mr. Marsh had a less sharply marked criterion of conformability than that employed by us in New Haven. As the result of all our numbers, we may say that the number of Leonids visible on the morning of the 14th of November, was probably about equal to, perhaps exceeding, that of the sporadic meteors. In view of the disturbing effect of moonlight this comparison is more valuable than any comparison with the absolute numbers counted in clear nights.
H. A. N.
ART. VIII.- On some phenomena of Binocular Vision; by JOSEPH
LECONTE, Prof. Geol. and Nat. Hist., Univ. of California. *
IV. The mode of representing the position of double images.
It is well known that if two objects, as a finger of each hand, be placed one beyond the other in the median line of sight, when the eyes are fixed upon the nearer object the farther object is seen double, the images being homonymous, i. e. on the same side as the eyes to which they belong: and when the eyes are fixed upon the farther object the nearer object is seen doubled, the images being in this case heteronymous, i. e. opposite the eyes to which they belong. These familiar facts are usually represented graphically as follows: Let R and L, figs. 1 and 2, represent the right and left eye, and A and B the two objects. Now when the eyes are directed upon A, fig. 1, then the light from B will impress the temporal halves of both retine and B will be seen by the right eye at b and by the left eye at b' (heteronymous); but if the eyes be directed upon B fig. 2, A will impress the nasal sides of the two retinæ, and be seen as homonymous images at a and a'. (In all cases in this paper objects seen single are represented by capitals, right eye images by plain italics, and left eye images by dashed italics). It will be observed that in both cases the doubled images are referred to a plane passing through the point of sight at right angles to the visual plane. For convenience I will call this the plane of sight Now every one who has ever tried the experiment knows that the double images are not thus referred in natural vision, but on the contrary are seen at their real distance, though not in their real position. The figures therefore though they truly represent the parallactic position of the double images do not represent truly their apparent distance. If on the other hand we attempt in our figures to refer the images to their proper distances, observing the law of direction, then they unite and form one; which is equally incorrect. It is evident therefore that these figures cannot represent truly the visual results.
The falseness of this mode of representation becomes much more conspicuous, if instead of two points or small objects, we substitute a line or rod. In this case the absurdity of projecting the images on the plane of sight is so evident that it is never attempted. The universal mode of representing the visual result of a rod placed in the median line of sight is shown in the accompanying figures. Fig. 3 represents the actual position of the rod AB in the median line of sight, fig. 4, the visual result when the eyes are directed upon A, and fig. 5 the visual result
* For the preceding articles on this subject, see II, xlviii, 68, 153. Ax. JOUR. SCI.-THIRD SERIES, VOL. I, No, 1.- Jan., 1871.
when the eyes are directed upon B. Now it will be observed that in both these figures the image of each eye is coincident with the visual line of the opposite eye, and therefore makes an angle with its own visual line equal to the visual angle. But this is not true. Fig. 3 shows that it ought to make but half that angle. If these figures therefore represent truly the position of the images, as indeed they do, then they do not represent truly the visual or apparent positions of the visual lines. The truth is, in natural vision the visual lines are shifted as well as the images of all objects not situated at the point of sight, and to the same degree, so that their positions relative to the visual line are perfectly maintained in the visual result.
Figures constructed on the usual plan give correctly the position and distance of objects seen single, but fail to represent truly the place of double images. They are well adapted to express binocular combinations of similar objects or similar figures on the plane of sight, as in my previous experiments; and to some extent also in the stereoscope, but are unadapted to express the results of binocular vision of natural objects.
I propose therefore a new, and I am convinced, far truer mode of representing the results of binocular vision, applicable to all
I am satisfied that if this mode had always been used much confusion would have been avoided. Some preliminary explanation will be required to make the method clear.
If a single object, as a finger, be placed before the eyes in the median line of sight and the eyes be directed to a distant point, the object will be seen double, the heteronymous images being separated by a space exactly equal to the interocular space. Now, the nose is no exception to this law; the nose is always seen double and bounding the common field of view on either side. Again if two similar objects or figures be placed before the eyes in the plane of sight and separated by a space equal to the interocular distance, and the eyes be directed as before to a distant point, both objects will be doubled, but two of the doubled images, viz: the right eye image of the right object and the left eye image of the left object, will combine to form a single binocular image in the middle, while the right eye image of the left object will be seen to the left and the left eye image of the right object will be seen to the right. Thus there will be three images seen; the middle one binocular, the right one belonging to the left eye alone and the left one belonging to the right eye alone. Now, the eyes themselves are no exception to this law. In binocular vision the eyes themselves seem to double ; two of them combining to form a binocular eye in the middle which looks out between the two noses, while the other two are on either side beyond the noses. Each eye seems to itself to occupy the central position while it sees (or would see if the
nose was not in the way) its fellow on the other side of the nose.
In other words, in binocular vision when the eyes are fixed upon a distant object the whole field of view, including the parts of the face, is shifted by the right eye one half the interocular space to the left, and by the left eye the same distance to the right, without altering the relative position of parts. By this shifting it is evident that the two eyes with their visual lines are brought in perfect coincidence, so that identical points in the two eyes are perfectly united.
The outline of the field of view varies somewhat with the prominence of the nose, brows and cheek bones, but its general form is much the same in all persons. I give in the accompanying figure (fig. 6) a rude outline of the field of view in my own case, nn rr being the field of the right eye, and n'n' ll the field of the left eye, and the irregular space nn n'n' being the common field of binocular vision bounded by the outline of the nose nn as seen by the right eye, and n'n' as seen by the left eye. The circle E represents the position of the combined eyes in the center of the common field, 1 and the position of the two eyes as seen each by the other or rather as they seem each to the other. A vertical projection is shown in fig. 7. E being the combined eyes, n and n' the nose as seen by the right and left eyes respectively on either side of the common field, and I r' each
eye seen by the other. It will be observed that I have represented the eye on the extreme right by r' instead of t, and on the extreme left by l instead of l'. The reason is that these, like the two noses, are only heteronymous images seen by the two eyes respectively from their central position. As an organ of vision the two eyes occupy the central position only, but as an object each from this central position sees its fellow on the other side of the nose right and left. This vertical projection I shall use in all my diagrams representing double images. By its use, however, we may represent equally well the position of objects or images seen single at the point of sight. By this method the visual results of even the most complicated figures, not only may be represented truly and with ease, but may. be worked out a priori with the utmost certainty. The great importance of this a priori help will be appreciated by all who have made experiments in binocular vision, and who therefore know how easy it is to overlook, or rather how difficult it is often to perceive, many of our visual impressions.
As we have already stated, while we gaze at a distant horizon any object in the median line whatever be its distance is seen double, the space between the images being exactly equal to the interocular space. Evidently then the median line of sight