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Open Sights vs. Peep Sights To the Editor of the SCIENTIFIC AMERICAN : I am honored by having Mr. Walter Winans, one of the best known big game shots in the world, and the running deer champion, disagree with me as to the optical performance attaching to the use of open sights on the rifle (SCIENTIFIC AMERICAN, January 22nd, 1916, page 99). While agreeing with me in my review of the military rifle sights of the world in “ How a Rifle is Sighted,” Mr. Winans does not agree as to the details of the stages in aiming over open rifle sights. Mr. Winans' letter is an amusing example of the difference between what one does, and what one thinks one does. He states that he does not see the rear sight ever as blurry or fuzzy, nor yet sharply for an instant and then change his focus to the front sight, some 20 inches or so farther up the barrel and ergo in a different focal plane from that of the rear. He states that he entirely “ ignores the rear sight.” He states that without looking at the rear sight the front goes instinctively into the. right position in the notch, and then to the right spot on the game. Inasmuch as the description of his sighting applies properly and entirely to the peep sight alone, and never to the open sight so far as actual optics are concerned, we are impelled somewhat to examine into his statements. If we. could do with the open sight what he says he does then we would not condemn, as we do, the open sight. The open sight system of a rifle consists of a small bead or other form at the muzzle of the rifle, this usually about one sixteenth inch in diameter, and on the barrel of the rifle near the breech, and usually 20 inches to the rear, a bar of steel, with a notch cut in it, so proportioned as to show the front sight with a little light around it. The rear may have its notch in wide “ V” shape, or in narrow “ U “ notch according to the preference of the shooter or the peculiarities of the maker of the rifle, but always the principle involved is the same. This is that the rifle is correctly sighted when the front sight touches the mark in the right spot, and then is drawn into the notch in the rear sight in the position selected by the rifleman as his standard sighting. If Mr. Winans will consult his oculist he will learn that when one object lies in a plane say 12 inches from the eye, and another object in a plane 32 inches from the eye, the two cannot be seen sharply with the same focal adjustment of the eye any more than the two can be photographed sharply with a camera set for either one, and the lens wide open. Neither is far enough away from the eye to be in what is practically the hyperfocal or the universal distance of focus from the eye-lens. Ergo the optical portion of seeing either sight clearly consists of focusing distinctly for an instant on either one to the exclusion of the other. Or if one is seen sharply all the time, the other is seen, if at all, blurred and fuzzy as stated. That this is precisely what the eye has to do is proven by the fact that men on whom age is creeping, must abandon the open sight principle and use the peep, which does not entail this leaping of eye and change of focus from one sight to the other. Stiffened muscles of accommodation prevent this. The writer, as instructor in the militia, and as secretary of the ' strongest rifle club in this country and as “consulting arms expert” for Outing and other magazines for some years, has so repeatedly and so successfully prescribed the peep sight in place of the open for men with eye troubles, that he knows beyond peradventure of the success of such change. While target shooting entails finer sighting than does most big game- shooting, still target shooting is at a contrasting mark and so not so much more difficult in sighting process than is big game aiming. This being so let us consider the record of riflemen using open sights. The British have for years used the open sight on their service rifle, the Lee-Enfield. The United States has used the peep for years on its service rifles. The poor British rifleman, using this open sight, is compelled to use an “ orthoptic” spectacle to enable him to define front and rear sight sharply. This orthoptic consists of a steel plate set in an ordinary spectacle frame, and pierced in front of the eye with a very fine hole. In the finer grades this hole is adjustable in size with an iris diaphragm just as is the lens opening in front of the camera lens. In effect this sharpens up the vision and makes the focus of the eye nearer to the desired universal focus, just as stopping down a lens increases the depth of the SCIENTIFIC AMERICAN focus of the camera lens. This is a standard article of equipment in British rifle shooting. Despite even this freak aid to aiming, the American rifle team in 1908 visited Bisley and wiped up the ground with the British and other rifle teams in typical and prayed-for British weather. The American team used peep sights, the British team the open sights to their disgust. In 1912 the American team went to the Olympic games at Stockholm and there once more wiped up the Swedish earth with the British and every other rifle team using open sights. The British were not outgunned, their match ammunition was as good as ours, they were out-sighted, despite being possibly better in-. dividual shots than our men. So much for the accuracy of the open sight in tests that are open and above-board tests or sights. Now let us consider Mr. Winans' reported performance of ignoring the rear sight and seeing but the front one. In a rifle stocked exactly to fit the rifleman, fired with no great desire for high accuracy, and a rifle to which the rifleman is as accustomed as he is to his gloves, this is partially possible. Before accepting this dictum of what Mr. Winans says he does for what he really does—which are horses of different colors—let us consider the ballistics of the matter. In the case of sights 20 inches apart, a fair average for sporting open sights, we have a radius of 20 inches, a diameter of a circle of 40 inches, using the rear sight as the center from which we strike our circle, and hence a circumference of 123 inches. Inasmuch as a circle contains 21,600 minutes of angle, a minute of angle with our radius stated is just .0058-inch long on either. sight. A minute of angle includes one inch for each hundred yards of distance, accurately 1.047 inches. In other words the error of a minute of angle on the sights means the error of an inch for each hundred yards of range the mark stands from the muzzle. Ergo the error of .0058-inch in aligning the sights means an inch error at 100 yards, 2 inches at 200, etc. The width of the common front sight hunting bead, or 1-16 inch, includes with our stated sight radius practically 11 minutes of angle, because in decimals the width of the front sight is .0625, and the width of a minute of angle is .0058. Ergo if Mr. Winans makes the small error in aligning his sights of just the width of the small front bead, he puts his shot 11 inches wide at 100, 22 inches wide at 200, and 33 inches wide at 300, all of which is unhappily sufficient to miss the vital spot on a brute if not the entire body. Such errors in elevation are very easy to make, particularly as open sights are sensitive to changes in light, which make the notch more distinct and alter the apparent relation of front and rear. Half this error or half the width of the front bead or 16 inches error at 300 is not good shooting, and yet half this means but 1-32 inch in the position of the front sight in the rear notch. These being the figures and the performance pertaining to the use of the open sight, the reader of the SCIENTIFIC AMERICAN will agree that if Mr. Winans can pitch his trusty sporting rifle to his shoulder and without looking at or ever seeing the rear sight, place the front sight in the rear notch with less than a 32nd inch error each time, he must have a rifle fitting him to perfection or be very lucky or both. What Mr. Winans does do is to perform the operation of glancing at the sights so rapidly as to be practically instantaneous, but our armies are not made of a few million duplicates of Walter Winans, big game shot extraordinary, nor are military rifles made to fit like a suit of clothes as are the rifles of Mr. Winans. Such men have to aim slowly, have to fish for front, then rear, and cannot depend on long practice and well fitting rifle to enable them to practically ignore the rear sight. Hence the undesirability of the open military rifle sight. Using the typewriter has as much to do with sighting a rifle as using a typewriter has to do with trundling a wheelbarrow. In one case we become so accustomed to the keyboard that we write by “ touch,” training of the fingers to stay in certain position over a familiar keyboard. In the other we have a lot of men very unfamiliar with the rifle, compared with the experience of Mr. Winans, and they cannot use “ touch” and they must perform the operations of sighting as I have described them. And the greater their deficiencies of eyesight, the greater will be their error in sighting with open sights. The dictum of Mr. Winans as to the superiority of the open sight over the peep may seem very conclusive to Mr. Winans. The cold fact of a few hundred thousand American riflemen paying from $2 to $6 . additional for peep sights on their sporting rifles each year, would seem to throw some little doubt on the conclusiveness of Mr. Winans' findings. 401 The matter boils down to the fact that Mr. Walter Winans, a Baltimore American but thoroughly imbued with the conservatism of his adopted “ right little, tight little isle,” prefers the open sights because most British rifle makers prefer them and install them and most British hunters conservatively follow. The other fact still remains—that target riflemen, who desire only to hit what they fire at, American big game hunters in the proportion of two to one, the American ordnance department of the army and optical science all declare in favor of the peep sight. The open sight is efficient in spite of optical difficulties so long as the eyes hold out. The peep sight is efficient because it complies with optical facts and it is efficient regardless of the eyesight. EDWARD C. CROSSMAN. Los Angeles, Cal. The Auroras of Iceland To the Editor of the SCIENTIFIC AMERICAN : During the last two months, there have been some magnificent auroras visible here at Akureyri, notably during the former half of October and the latter half of November. On the 6th and 7th of October last, I observed some splendid auroral arcs crossing the sky from east to west, as usual a short distance north of this place and rising from 30 to 70 deg. above the horizon. From the 13th to the 22nd of November the auroras were extremely brilliant. Those of the 13th were particularly beautiful. Words alone cannot describe their beauty. Between 6 and 7 o'clock in the evening of that day, there appeared suddenly a stream, or wand, of light above the horizon and to the northwest of this town. In a twinkling of an eye this stream of light extended itself across the heaven forming an arc of continuous light even to the western horizon. The latter is formed by a range of mountains 1,500 meters high and 15 kilometers distant, while along the eastern horizon runs a heath about 1,000 feet in height and 6 kilometers distant. The arc of auroras crossed the sky just beneath the Great Bear (Ursa Major) constellation, and remained there growing in brightness for a few moments, resembling an immense band or fringe of light, made up of dazzling lances or spears of ethereal flame moving from east to west and west to east like a vast line of infantry. Then, this arc was paralleled by another which crossed the Ursa Major constellation; a third crossed by the Pole star; a fourth crossed the ' zenith (Akureyri is situated on 65° 40 north latitude) ; a fifth a little to the south; and a sixth and a seventh arc crossed by the Pleiades. The seven arcs formed a bridge of continually moving light completely across the heavens. This continued for some 10 to 15 minutes, during which time the auroras assumed at times various colors reflected by the moonlight. Then the most northerly iirc faded away as did also the most southerly arcs, but the second, the third and the fourth arcs remained a few moments longer, when they broke up and rolled themselves into a vast spiral of dazzling light which outshone the stars and hid from view the cirrus clouds immediately above it. A similar though less brilliant display greeted the eye on the 14th, the 15th and up to the 20th of November between 6 and 8 o'clock in the -evening. On the 21st, three young men of this town saw, about 6 :15 to 6 :30 in the evening, a brilliant stream of light dart up above the eastern horizon, • and then form an arc of light across the sky just above the Great Bear, but below the Pole star. After remaining a few minutes the arc rolled itself up into a spiral of light of great brilliancy which displayed all the colors of the rainbow. From 6 :30 until 8 :30 that evening I, myself, observed some very brilliant auroras, but the rainbow tints were not generally visible, these being probably due to re, flected moonlight. At times the auroras were bright enough to hide some cirrus' clouds immediately above them and were therefore at a lower elevation than these, but they were decidedly above the cumulus clouds which covered part of the sky. The height of these auroras has therefore been between 3,000 and 9,000 meters, and the' most northerly arc which rose to 30 deg. above the horizon has only been some 12 kilometers or good seven English miles north of this place. The auroral displays are most frequent and most brilliant in cold and clear weather and seem periodical. Many reasons lead me to suppose them to be emanations of terrestrial energy rather than of solar energy. As yet there is no station of any value in Iceland although industrial, commercial and scientific interests demand one, as also an astronomical observatory, both here and in the southern section of the island. FRIMANN B. ABNGRIMSSON. Akureyri, Iceland.
