FRAGMENTS OF SCIENCE. 



861 



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 ma- 

 hogany 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 consider- 

 able intervening air space, and through gela- 

 tin, gutta-percha tissue, collodion, and cellu- 

 loid. 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 mo?t ac- 

 tive 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 

 Tth, 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 be- 

 fore his death he intended to be present at 

 the meeting of the American Association 

 just held in Boston. His fame was world- 

 wide, and his eminence as one of the leading 

 geologists of his time was very generally rec- 

 ognized in Europe as well as in Ameiica. 

 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 ne- 

 groes of Farmville, Va., contributed by Mr. 

 W. E. B. Dubois to the Bulletin of the De- 

 partment 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 indus- 



trious, 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 ques- 

 tion 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 threaten- 

 ing." One of the most encouraging signs is 

 that "the whole group life of the Farmville 

 negroes is pervaded by a peculiar hopeful- 

 ness 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 pre- 

 pare for them. As I regard it, the work of 



