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its most perfectly normal condition to have good visual power. A person so blind with cataract as to only tell light from dark will appreciate quite pale shades of color. In the centre of the retina is a zone where all of the three base colors now generally accepted, red, green, and violet, are perceived ; next outside of this a zone where only green and violet or blue are perceived, and beyond this another zone where blue alone produces its effect. The so-called Young-Helmholtz theory of color perception is, that there are three sorts of nerve fibres or retinal perceptive elements which receive or are sensitive to these three colors, red, green, and violet. The greater or less stimulation of these in different proportions is supposed to give us all the variations of the colors. This theory has been used in the explanation of colorblindness, which is considered to be either red, green, or violet blindness. The first two mutually include each other, and the last implies blindness to yellow, as well as to violet or blue. The adoption of this theory in conformity with the best and highest authorities, or of the theory of Hering, is of no importance in reference to the practical relations of color-blindness. Theories explain but do not alter facts. Facts prove that there are persoos blind to red and green, or to yellow and blue or violet. Red and green blindness are much more common. Violet blindness is a very rare occurrence, but nevertheless has been found. What proportion of people are color-blind has been the subject of much discussion and debate. Since Prof. Holmgren has put into the hands of experts a very simple and ready method of detecting it, large numbers of persons of either sex have been tested in Europe and also in America. I have examined over thirty thousand individuals, with the result of finding about four per cent. of males color-blind, whilst with females it is an extremely rare occurrence. Age, nationality, social condition, civilization or education have nothing to do with it. It is hereditary, incurable when congenital, and can be but slightly palliated by artificial means. It may be produced by some diseases of the brain, by injuries of this organ, and by poisoning from alcohol and tobacco. A case has been recorded of unilateral congenital total color-blindness in a young lady belonging to a color-blind family. The normal eye may be rendered hypnotic, and then becomes color-blind. The con. genital color-blind eye may be rendered temporarily normal, also by being put in a hypnotic state. These peculiar conditions are at present receiving great attention from physiologists.

Different observers in various parts of the world having now established the fact that four per cent. of males are more or less color-blind,

it will naturally be at once asked, How is it that this has not been known before? The answer is that with previous methods of examination they have escaped detection, whilst only since accurate and ready methods have been introduced was it possible for experts tomas nowexamine large numbers with any scientific method. The manual above spoken of must be referred to in explanation of how the colorblind escape detection. The limits of this article prevent entering into it here. It is a curious study by itself. That the color-blind have eluded and do escape detection is one source of danger from this defect. It requires a pretty thorough knowledge of the physiology of the color sense, and an acquaintance with the vision of the color-blind to enable even medical experts to grasp the whole force and meaning of a chromatic defect of the eye. When color-blindness is spoken of, it means generally red and green blindness, or red-green blindness, as some would call it. This only interests railroads, whilst at sea violet-yellow blindness is also important in relation to the colors of signal flags. As remarked, this species is extremely rare. A person color-blind sees, in the proportion he is blind, all his bliud color and its opposite (red and green) so much darker; or, rather, so much like gray, or a neutral color. The darker the color the darker the gray. For example, very dark red or green becomes black, et cetera. Hence a red light becomes a white one, very day

A red buoy cannot be distinguished from a black one. A red signal light or lighthouse seems simply a dim white light. The colors of the side lights are confused or wholly gone. A naval officer slightly green-blind remarked that at a distance where the red light seemed marked in its color he could not distinguish the green light from the mast-head light. The difficulty of appreciating this on the part of those to whom it is new, has naturally been a serious drawback to the introduction of the very necessary examinations for the detection of color-blindness, and the elimination from posts of danger of those who are thus afflicted. The color-blind should not be, of course, allowed to enter the navy in any position where their want of color perception will be a source of danger to the vessel.

To the laity nothing would seem more simple than asking a person the names of colors in order to ascertain whether they were color-blind. Yet, as Prof. Helmholtz has well shown, this is perfectly useless, and as Goethe long ago said, such testing will but make the examined and examiner crazy. What we need is some method by which we can find the exact effect of the color on a person's brain. This we can do if we

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require them to match a given color from a collection of colored objects. This method of comparison is alone of avail. Of those suggested none is more simple or surer than that suggested by Prof. Holmgren and now adopted in the U. S. Army, Navy, and Marine-Hospital Service. It is by colored worsted, and is described in detail in the manual above referred to. A mutual language of examiner and examined is not necessary. Any wild or uncivilized tribes may be tested by naval surgeons, whenever met during the voyage, thereby gathering for us valuable ethnological data as to the color sense and its development. I employed it in my testing the students of our colleges and scholars of our schools, also railroad employes and officers and sailors. The text-book and worsted do not occupy eight inches square and can be carried and used anywhere in fair daylight. Other additional methods of deciding quantitative color perception are of course employed by medical experts in deciding cases. Those of Prof. Dondas and Prof. Holmgren, described in my book, are some of the best and most practical, being employed on the railroads of Sweden and Holland. Naval surgeons can however readily learn de visu how to detect color blindness with certainty by Holmgren's worsted test.

By reference to my volume it will be seen that several maritime nations besides our own have recognized the dangers of color-blindness on the ocean, and established regulations to control it in the navies and merchant marine. A vessel of one nation with no color-blind on the lookout will not avoid a collision when meeting that of another nationality from whose personnel those defective in their color sense have not been eliminated by expert examination and strict laws. A petition to Congress, in favor of which I argued before the Naval Committee, has been presented, asking their "consideration of a general law of control in the navy and merchant marine, of color-blindness and visual acuteness, and the agreement by an international commission of definite and uniform standards of testing these necessary qualifications."

NAVAL INSTITUTE, ANNAPOLIS,

Mar. 11, 1880.

LIEUT.-COM'DR HARRINGTON, U.S. N., in the Chair.

DISCUSSION.

A UNIFORM SYSTEM OF RIGS for BOATS AND LAUNCHES.

war,

THE CHAIRMAN:

The subject before the Institute is one of importance to the Navy; for it does not appear that experience has produced in our service a system of boats and their sailing equipments. And, while the greater force of opinion inclines towards one rig as the best for cutters, the varieties of preference are not less numerous than the classes of boats and sails in use.

Safety, carrying capacity combined with fair speed, and capability of united action in fleets, are prime qualities in boats as in ships of

In the organization of a system of boats for a man-of-war, the pumber and dimensions having been determined, the equipment should be designed to secure unity and precision in maneuvering under oars or sail. The classes of boats being reduced to the lowest possible num. ber, and a uniform plan of equipment employed, the ships of the Navy will meet on even ground in that respect. I shall not enlarge upon this idea, but I consider it an important one; and I would carry the practice so far as to make the equipments of uniform size and interchangeable for the same class of boats.

A noiseless exhaust of steam being secured in the steam launches, the requirements of the torpedo service properly controls their equipment. Should spars and sails be supplied for use when abandoning ship, they ought to be of the same pattern as those for the sailing launches; and, in readiness for such an emergency, the boat should be stowed without its boiler.

Gigs, dinghies, and catamarans, of small carrying capacity, and not of the line of service boats, may be fitted as desired, and will furnish sufficient scope for the American desire for speed and novelty.

The service boats may be considered as of two classes, viz.; launches, and cutters; the former including the steam launches when used with. out boilers, and the latter the whale boats. One size of whale boats, and two or three each of cutters and launches, should be sufficient; the dimensions of each size being enforced by regulation for all new boats.

I am of the opinion that launches should be rigged as sloops, the boom being fitted always with a topping lift. The gaff topsail is worthless in such boats, and works contrary to the rule of simplicity and handiness. Let us have as little gear as possible in our boats.

I prefer for all other service boats the rig known as the sliding gun. ter, regarding it as safe, economical, handy, and sufficiently powerful. The shape of the principal sails in this rig, that of the leg-of-mutton, has found favor among boatmen almost everywhere. The centre of effort is brought low, whatever amount of canvass is spread, by altering the length of the masts and the foot of the sail; and reefing is accomplished in a moment. For the foremast, a slot should be cut in the foreand-aft piece, abaft the mast hole, and a guide board placed under the thwart, extending from the forward edge of the mast hole to the step, and flush with both. In making sail, the heel of the mast, pointed through the slot, slides upon the guide board and passes into the step without delay. The slot is then closed by a close fitting chock. For the main mast, the slot is cut and the guide board placed upon the opposite side. With these arrangements, the short lower masts of the sliding gunter are most readily shipped and unshipped. In point of speed, there may be a slight difference in favor of the lug or the sprit sail, but I doubt it; and if such is the case, the superiority in that respect is obtained at the expense of the more important qualities of handiness and safety. There is another small argument in favor of the sliding gunter, which will appeal most to the Executive Officer. In a somewhat extended experience in that capacity, I have found that boats with the sliding gunter require, generally, fewer repairs for accidental injuries. The masts and topmasts are seldom broken, or carried away in use; and the boat gets few hard knocks, which may or may not be due to the superior handiness of boats with that rig.

I regard the sprit sail as unworthy of use. The dipping lug, used with a jigger, is still the regulation sail for cutters in the English Navy. It is an admirable sail in many respects, and appears to suit the broader English boats. The Forbes rig for cutters, illustrated by the drawing on the board, is a modification, apparently, of the lug sail, and, judg. ing from the drawing, I should say it is a great improvement. It appears to obviate the necessity of dipping.

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