periment was followed by Wollaston in England about the same time, while he in turn was followed by a great host of workers from amongst whom we only mention such as Sir John Herschel, Hunt, Becquerel and Niepce.

All these workers had been striving after the reproductions of color in one print, but now comes the name of Du Hauron who in 1859 had delivered a lecture in which he foreshadowed the color photography of the present, and it was in 1869 he published a volume which contains all essentials for success in the three color process, not only by the superposition of colored images, but also by the colored line system which has more recently been elaborated by Prof. Joly, of Dublin University, and by the late Mr. McDonough, of America, while to the labors of Frederic E. Ives, of Philadelphia, the adaptability of the present day three color process is greatly indebted.

When a pencil of white light is passed through a prism the beam is broken up and changed into a broad band, which is composed of the seven colors-red, orange, yellow, green, blue, indigo and violet, which merge imperceptibly into one another, and from the mixture of these seven every shade or tint of color in nature is produced. But it has also been discovered that it is not necessary to have the entire seven, as these same various tints and shades can be duplicated by three, a red, a green and a riolet, there being actually only three sets of color perceptive organs or nerve terminals in the human eye. Each of these terminals being constituted to receive an impression of one tint of color, these three nerves whenever acted upon equally produce the sensation of white; now, this being clearly understood, the general methods of color photography may be stated.

Three negatives are produced by red, violet and green light respectively, and the nearer these lights correspond to the primary tints which excite the color sensation in the eye, the better. The prints from these negatives are superposed either by optical projection, or by the laying out of minute parts of each, side by side, in lines, each line or tint of the original being closely matched to the color used in taking the negatives primarily. When printed on paper, either by hand methods or by the printing press, then the colors must be complementary to those used in making the negative, viz: red, yellow and blue.

In practice, it was found that the question of the making of the negatives by the colored lights was very much complicated, owing to the fact that there was no plate which would correctly represent the spectrum in its varying luminosities; in fact, that certain regions of the spectrum could not be photographed at all, owing to the fact that the plate was sensitive only to the blue and violet of the visible spectrum, and also to a considerable extent to the region extending far beyond that visible violet, and known as the ultra-violet. This difficulty was eventually overcome by the discovery that certain of the organic dye stuffs conferred upon the plate dyed in them, a selective color receptivity, and at length led to the enunciation of the law, that "a plate is acted upon by the color which it absorbs." Therefore, to confer a spe cial sensitiveness, say, to the red color of the spectrum, all that is necessary is to dye the

film in blue, or if the plate be desired sensitive to green, then the dye is red; by combining the blue and red dye in proper proportion it is pos sible to render a plate sensitive to the entire range of the spectrum, in fact such plates are now manufactured in both England and France for the market.

In the process of methods which have been placed before the public as commercially successful that of McDonough is assuredly the most ingenious and perfect, and the almost unvarying uniformity of results has rapidly placed it in the hands of the serious photographer of both amateur and professional class, while in the matter of window transparencies, or substitution of stained glass, it certainly offers a class of subjects which for truthfulness and beauty of effect leave little to be desired. Briefly considered the details of the process are as follows:

A sheet of glass is ruled with parallel alternate lines or bands of transparent red, green and blue-violet, at a gauge of about three hundred lines to the inch, which colors are selected to closely approximate the three primary color sensations. This ruled screen is placed in the camera immediately in front of and in contact with the surface of the sensitive plate, which plate has been dyed so that it is sensitive to all colors of the spectrum. Now when we photograph, say, a green leaf, which for the purpose of explanation we will assume as reflecting green light only, the color has to pass through the green ruled lines of the screen before it can reach the sensitive surface of the plate, the blue-violet lines stop all color from passing through them except blue light, and as our object is only reflecting green light, no light therefore reaches the plate immediately behind and in contact with the blue-violet lines in the screen, the red lines, in the same way, stop all light but red, and as we have in the present instance only green light, therefore no light reaches the plate in those portions which are immediately behind the red lines, so that we have a full action through one set of linesthe green, and no action at all through the remaining two sets, the blue and red.

When such a plate is developed we find that the only effect we can obtain is that of deposit in the places which were covered by the green lines, with transparency or entire absence of deposit in the spaces covered by the blue and red lines.

Taking now this negative and making therefrom a positive, by contact, we will obtain a plate exactly the reverse of the negative and in which the blue and red spaces will be opaque with deposit, while the green will be represented by clear glass, and the only thing that remains now to be done is to place the transparency in contact with the ruled color screen in order to obtain the correct representation of the object photographed, for, as we have the blue and red lines opaque on the positive, these colors are covered over, or blotted out, and only the green remains to be carried through the transparent portions of the positive.

In actual practice there are but few differences from the bare outline as given above, although there were many difficulties which had to be overcome before the process reached its present state of perfection.

First, in the ruling of the colored screen a special engine had to be built to guarantee accuracy in the spacing and width of the lines and uniformity of the flow of color. This item demanding special care so that the color lines should neither overlap on their edges or show spaces, to say nothing of the difficulty of obtaining a line which should possess the same strength of color at the end as at the beginning. Then, although the plate has been dyed to render it sensitive to the entire spectrum, yet, the action of the blue is still by far the stronger, and the balance of color was destroyed. This difficulty was overcome in the most ingenious manner by the adoption of a "chromatic-balance shutter," which is fastened in front of the lens, and which consist of two thin films of yellow dye, on mica, which, by a clever arrangement, is made so that the depth of tint can be varied at will and as occasion requires, with the result that the yellow absorbs or retards the action of the blue light, thus allowing the red and green to "catch up," as it were, and impress themselves with equal strength when photographing a white: the lines themselves being almost imperceptible owing to the fineness of the ruling the three colors strike the eye in such close juxtaposition that they are absorbed as a mixture of the three lights, thus producing white.

Again, it was found that the screen through which the negative was made originally was not suited exactly to act as a perfect “viewing screen,' so that this difficulty resolved itself into the necessity for a negative or analytical "taking screen" and a positive or synthetical "viewing screen," which latter differs somewhat in the color absorption from that of the former.

The results of this process are of a truly marvelous beauty and excellence and the ease with which the operations are performed has rapidly advanced it to a place in the foremost rank of color methods.

Next in turn comes the Ives process, which, like that of McDonough, depends upon the admixture of colored light. Briefly described:

Three separate negatives are made by the action of the three primary colors through colored light filters, and from these negatives are made three positives, which are backed by colored glass of a somewhat different tint from that used in making the negatives. The red positive is backed with red glass, the blue with blue, and the green with green, in a special contrivance named the "Kromskop" and by an arrangement of transparent mirrors the three colored images are caused to superpose and combine, the one upon the other, and, viewed through an observing lens presents to the eye an image in natural colors. The Kromskop is made either monocular or binocular, and in the latter case the object not only presents itself in color, but also with that relief which is so charming in stereoscopic vision. There is also due to the untiring energy of Mr. Ives the advantage of being able to take the three primary negatives in one operation by the aid of a special camera which splits up the light into three colors of measured luminosity, thus greatly simplifying the operation.

The results are very beautiful, especially when in place of the Kromskop use is made

of three lanterns, and the object or view projected upon a screen: here there is no "lining" to mar the view, and the three colored lights mix in perfect homogenity.

We now come to the reproduction of natural colors on paper, or other suitable support. Here the process differs considerably from that which we have described. True the three negatives are made in the same manner by the action of specially selected color filters upon plates which have been sensitized for colors, but from there on the mode of procedure must be greatly altered. Hitherto we have built up our analysed negatives by the admixture of colored light, either by juxtaposition of colors, or by superimposition, but now we are no longer dealing with light, but with pigments.

If we take a beam of white light as representing a luminosity of 100, then when we divide it up into a spectrum by passing it through a prism, it stands to reason that the various colors must represent certain amounts of that 100 according to their hue, and if we suppose, for the sake of argument, we take each of the three primary colors, viz., red, green and violet, as of equal luminosities, then each color represents a value of 33 1-3 the luminosity of white light. When we mix green light and red light together we have simply added two equal quantities of light averaging 331-3 each, and obtain, as a result, 66 2-3 luminosity of yellow light; then, if we further add to this resultant yellow the remaining portion of blue-violet, we are adding just 33 1-3 more, obtaining 100 of white light, but with the mixture of pigments we pursue an exactly opposite course, not adding light to darkness, but darkness to light.

When an artist paints a picture he takes the white paper which represents the highest light or luminosity which he has at his com mand, and which appears white because it reflects all the colors in white light, and to that white surface he adds pigment color, thereby darkening or taking away the light from certain portions. Suppose, for example, he covers one-half of the paper with a wash of the purest yellow transparent pigment he has, that half will appear yellow because he has covered it with a material which absorbs all the light which passes through it except the yellow, which it reflects to the eye. As the pigment or material has, as just stated, absorbed all of the light save the yellow, it therefore follows that that yellow must represent only a portion of the entire luminosity of the white paper, with the result that the paper has been darkened-he has taken away from the paper some portion of its reflected light, and were he to paint a patch of red, green and violet color one over the other, the result would be black, because all the rays of the white paper would be absorbed before they could reach the eye.

In actual practice the three primary negatives (the color records) are taken, and from them are made three positives, and from these positives there are made three more negatives, with the interposition of a ruled cross-line screen between the sensitive plate and the lens, which breaks the image up into varying sizes and shapes of dots, thus giving a printing surface or grain which enables it to be reproduced in all its tones. These latter screen negatives are now printed upon copper, and etched

until they are sufficiently deep for printing from, and then put upon the printing press. The plate which was made from the negative taken through the blue-violet filter is printed in yellow, then that which was made from the negative taken through the green filter, is next printed, and in red, while the remaining plate, made from the negative taken through the red filter, is printed in blue-the result, when all these printings are completed, being a reproduction of the object originally copied.

"But," it may be asked, "why is the violet negative printed in yellow, the green in red, and the red in blue?" The reason is very simple. In a black and white subject, there are two parts complementary to one another, which are, white paper, for one part, and white paper covered with black pigment, for the other part; a negative of this subject will also consist of two parts, respectively, opaque and transparent, the opaque parts corresponding to where the light has acted, and the transparent portions representing the black pigment or where there has been no light action.

When a print is made from such a negative the materials are-white paper-and a pigment which will absorb white-black. The transparent portion of the negative prints this color, while the opaque portions have no part (that is, no active part) in producing the print. Thus it may be said that the negative is made by white, but prints in black, viz.-the complementary color; in printing therefore from color negatives the printing ink is complementary to the part of the object which photographs.

It is impossible in the space at command to do more than even mention any other process. That of Prof. Wood of the University of Wisconsin, although undoubtedly very fine, is as yet not adapted to the general worker, or to any further consideration than as a beautiful and clever laboratory experiment. At any rate, its many technical points which have yet to be overcome do not warrant it a description here.

In concluding this article we may state that no attempt has been made to handle the subject in an exhaustive manner, but only to present as it were, the skeleton, from even the superficial study of which some clear idea may be deduced of the general methods in vogue at the present day and which are handled with success and profit by those interested in their public acceptance. R. JAMES WALLACE,

Photographic Research Laboratory, Elgin.

POLAR EXPEDITION, ANTARCTIC.-On Aug. 6, 1901, the British Antarctic ship Discovery set sail from Cowes. King Edward VII., who is deeply interested in the expedition, inspected the vessel prior to her departure on her trip of three or four years' exploration of the Antarctic circle. The Discovery is commanded by Captain R. F. Scott, Royal Navy, late of the Majestic. Dr. George Murray, of the British Natural History Museum, goes as editor of the scientific results, and will probably be appointed director, as Professor Gregory has resigned.

The civilian scientific staff consists of Dr. R. Koettlitz (surgeon and botanist), Dr. E. A. Wilson (surgeon, zoologist and artist). Mr. T. V. Hodgson (biologist), Mr. H. T. Farrar (geologist), who is also an expert physicist and chemist, and Mr. Louis Bernacchi, who was on the

Newnes-Borchgrevink expedition, and who is a specialist in terrestrial magnetism, a trained meteorological observer, as well as an efficient surveyor. Officers and crew number forty-eight. The German steamer Gauss, bearing the German Antarctic Expedition, sailed somewhat earlier, leaving Kiel August 11. This is under the leadership of Prof. Eric von Drygalski. of CAPT. R. F. SCOTT, R. N. Berlin. (See DRYGALSKI, Commander of the British page 51.) Expedition.

The scientists accompanying the expedition are Dr. Ernest von Hoeffen, of Kiel, zoologist and botanist; Dr. Hans Gaezart, of Munich, bacteriologist: Dr. Emil Phillippi, of Breslau, geologist, and Dr. Friederich Biedlingmaier, of Lauffen, meteorologist.

Scandinavia is to co-operate with Germany and England in this great scientific venture. The good ship Antarctic was to have left Sweden very soon under the leadership of Dr. Nordenskjöld (see NORDENSKJÖLD, page 385), but the sudden death of this accomplished explorer will greatly change the plans of the Swedes and may delay the starting of the expedition for a time.

It is probable that a Scottish expedition will co-operate in this important department of research. This was expected to sail in September under the leadership of Mr. W. S. Bruce, its sphere of operations being to the southeast of Cape Horn and west of Graham Land. There appear to be some difficulties in the way of starting, but it is hoped that they may be over

come.

Thus it will be seen that the problems of the Antarctic circle will be attacked this year by three, and perhaps four, European expeditions.

This is the first time that so powerful a combination has been brought to bear upon the frozen secrets of either pole or of any other unknown region. The interest in the scientific world is therefore widespread, and even the Argentine Republic proposes to assist by establishing, contemporaneously, a post of scientific observation somewhere on the south of Tierra del Fuego.

The great expeditions will work together. although they will at times be thousands of miles apart, and from this collaboration valuable results are expected. After the return of the German Deep Sea Expedition, negotiations were entered into between the British and German authorities in such matters, which culminated at the Seventh International Geographical Congress, which was held in Berlin in October of 1899. A complete understanding was here arrived at concerning the route and scope of the German and British expeditions. To understand clearly what it is proposed to do, a brief consideration of a South Polar chart will be useful. It would then be seen that the Polar circle is bounded to the north by three oceans-the Pacific, the Indian and

DR. E. VON DRYGALSKI.
Leader of the German Expedition.

the Atlantic-which south of the latitude of Cape Horn, become one great sea, encircling the earth and the Pole. Bounding this water area and roughly trisecting the ocean on the north, are the southern extremities of the continents of Africa and South America, and of the island world of Australia, New Zealand, and Tasmania, while island groups lie scattered between. Of these it is important that we should remember Kerguelen Island, which is intersected by lat. 49° S., long. 69° 30' E., midway between the Cape of Good Hope and Cape Leeuwin, in West Australia, the South Shetland Islands, and Graham Land. south of Cape Horn, and Victoria Land, some 2,000 miles directly south of New Zealand, because it is at these points, which trisect with tolerable exactitude the South Polar circumference, or at no great distance from them, that the three or four Antarctic expeditions will take up their winter quarters.

The accompanying map of the Antarctic Lands and Seas will show that very little land has been located and named in these frozen wastes.

Lying to the south and east of Tierra del Fuego are groups of islands like the South Orkneys and South Shetlands, which though well outside the Antarctic circle, are virtually Antarctic in their condition.

South of Cape Horn is Graham Land, a bit of coast which is supposed to be a part of the Antarctic Continent. Southwest of this is another island or coast, which is called Alexander Land. There is little else which has been definitely located until far to the west and south we find the scene of Sir James Ross' explorations, nearly sixty years ago; but much of this long route is faced by a great ice barrier, behind which it is supposed that unknown lands may lie.

South of New Zealand we find the longest piece of Antarctic coast land which has been laid down with certainty, and we may say that from 160° W. to about 160° E. there is a practically continuous coast line stretching from about 70° to 78° S. West of this bits of land have been laid down upon the maps on the authority of Wilkes and D'Urville, but these have not been identified by succeeding explorers. In the longitude of Southern Madagascar we find Kemp Land and Enderby Land, but they appear to be insignificant in extent.

The British ship Discovery has cost $250,000, and although built entirely of wood, she is

considered far stronger than any ordinary navigating boat. Iron was barred from the vessel's construction in view of the fact that one of the main objects of the expedition is magnetic survey work of a most important character. She is so built that when the ice pack closes in upon her she will rise and clear herself away. If the rudder and propeller are threatened both can be hauled on deck. She has air locks between her exterior and interior, so that those who enter and leave her will not disturb the warm atmosphere that will comfort those within the ship.

Her cabins, workrooms and laboratories are of the best construction, and her storerooms are capable of holding food for her crew, numbering forty men, for three years. She goes out under the auspices of the Royal Geographical Society and of the Royal Society. The

Government has co-operated by granting the free services of naval officers and men, besides a substantial sum of money from the Treasury. Her equipment includes the Röentgen Ray and the wireless telegraphy of Marconi. With a view to circumventing, if possible, the great ice barrier, the Discovery carries a balloon apparatus. She will proceed via Australia and New Zealand to Victoria Land, where Borchgrevink, with Sir George Newnes' expedition from the Southern Cross wintered in 1899-1900, and from which they made the Antarctic record of latitude 78° 34' S., the farthest southern point which was ever reached by man.

Mr.

The Discovery will probably sight the ice-pack in December of the present year, when the whole navigable season of the Antarctic summer will be passed in exploration in the ship. which will proceed south along the east coast