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FRAGMENTS OF SCIENCE.

when left in contact with the plate for a week, formed an image so exact that minute scratches were reproduced; the structure and rings of growth from the section of a pine tree, and even the grain of a piece of mahogany which had been in practical darkness for a couple of centuries, were transferred to the plate, with perfect fidelity. It was also found that actual contact was not necessary, the plate being affected through a considerable intervening air space, and through gelatin, gutta-percha tissue, collodion, and celluloid. Glass was found to be quite impervious. The emanations from certain uranium salts were found, however, to pass through the glass to some extent. Among the most active metals are zinc, magnesium, aluminum, nickel, lead, and bismuth. Copper and iron are practically inert. Strawboard and fresh charcoal and copal varnish act very strongly upon the plate. Pure mercury is inactive. For efficient and rapid action, a fairly high temperature (55° C.) and a perfectly clean metallic surface are necessary. Dr. Russell's views regarding the cause of this action are not definitely stated, but he seems to incline toward the theory that the effects are due to vapors given off by the objects.


MINOR PARAGRAPHS.

Dr. James Hall, the veteran geologist, one of the last survivors of the pioneers of the science in the United States, and one of the founders of the American Association, died at Echo Hill, Bethlehem, N. H., August 7th, at the ripe old age of eighty-seven years. Notwithstanding his advanced age, he was able last year to make the long journey to Russia to attend the International Geological Congress. After his return thence his health began to fail, but until a very short time before his death he intended to be present at the meeting of the American Association just held in Boston. His fame was worldwide, and his eminence as one of the leading geologists of his time was very generally recognized in Europe as well as in America. Two years ago the American Association, in Buffalo, devoted a special session to his honor. An account of his life and his work in geology was published, with a portrait, in the Popular Science Monthly for November, 1884. An account, contributed by him, of the New York State Geological Survey, his chief scientific achievement, will also be found in the Monthly for April, 1883.

Among the results of a study of the negroes of Farmville, Va., contributed by Mr. W. E. B. Dubois to the Bulletin of the Department of Labor, is the conviction of a growing differentiation of classes among these people. The study brings to light facts favorable and unfavorable, and conditions good, bad, and indifferent. One visitor might find these people idle, unreliable, careless with their money, and lewd; while another would say that they were industrious, owners of property, and slowly but steadily advancing in education and morals—according to the particular group to which his attention was most directed. The question is not whether the negro is lazy and criminal, or industrious and ambitious, but, rather, "What, in a given community, is the proportion of lazy to industrious negroes, and what is the tendency to development in these classes?" Bearing this in mind, it seems fair to conclude, after an impartial study of the Farmville conditions, that the industrious and property-accumulating class of the negro citizens "best represents, on the whole, the general tendencies of the group. At the same time, the mass of sloth and immorality is still large and threatening." One of the most encouraging signs is that "the whole group life of the Farmville negroes is pervaded by a peculiar hopefulness on the part of the people themselves. No one of them doubts in the least but that one day black people will have all rights they are now struggling for, and that the negro will be recognized among the earth's great peoples."

The recognition by Mayor Quincy, of Boston, in his welcoming address to the American Association, of the value of science in civic administration was only just, but of a kind that is rarely offered from the official side. "Your work," the mayor said, "has a very direct relation to the work in which the people of the city of Boston are engaged in their corporate capacity and the work which their municipal government is trying to prepare for them. As I regard it, the work of