of hyposulphite of soda and a mercurial compound in such proportions that the bisulphide of mercury is slowly deposited, the deposition being almost entirely suspended until the print containing the unreduced chloride of silver is added to the solution. The withdrawal of hyposulphite to dissolve the chloride causes the deposition of the bisulphide to take place in the print." Pictures obtained in this manner resist strong reagents in a way that gives promise of great permanence, while they have a rich tone, and a novel and fine effect. Mr. Sherman has been experimenting a good deal on the precipitation of vermilion, and finds the color of the product powerfully affected by light.
THE SUN'S ATMOSPHERE.
Dr. Janssen, the French astronomer, in a letter to Prof. Newton, of Yale College, an extract from which is published in the American Journal of Science and Arts, says of the sun's atmosphere: "My observations prove that, independently of the cosmical matter which should be found near the sun, there exists about the body an atmosphere of great extent, exceedingly rare, and with a hydrogen base. This atmosphere, which doubtless forms the last gaseous envelope of the sun, is fed from the matter of the protuberances which is shot up with great violence from the interior of the photosphere. But it is distinguished from the chromosphere and the protuberances by a much smaller density, a lower temperature, and perhaps by the presence of certain different gases." Janssen proposes to call this the "coronal atmosphere," as he considers it to produce a large portion of the phenomena of the solar corona.
SCIENTIFIC ADVANCE IN GERMANY.
Prof. Virchow, in his address before the Congress of German Naturalists, states some facts which show what progress freedom of discussion has made in Germany since the beginning of the present century. "Not perhaps at the dead of night, but still beneath the veil of secrecy, a handful of savants assembled for the first time at Leipsic, at the invitation of Oken. In fact, in 1822, no considerable body of men could come together in Germany, in answer to a public invitation, with the permission of the civil authority. They could not discuss among themselves scientific questions, no matter how unconnected with the political and national questions of the day. Add to this that other fact, that, if I am not mistaken, it was only in 1861, at the Congress of Naturalists at Spires, that the names of the Austrian members could be made public, and then we can appreciate the tremendous change that has been brought about in Vaterland." In the same address Dr. Virchow pays a well-earned tribute of honor to French savants. He opposes also the suggestion that has been made by certain German professors, that brevets, or honorary memberships of French Academies, etc., held by German scientific men, should be sent back, for the reason that a distinguished French botanist had recently declined the honor of being made an associate of the Natural Science Academy of Leipsic.
ACTION OF SEWAGE-GAS ON LEAD PIPES.
Dr. Andrew Fergus states that lead soil-pipes are often found corroded and even perforated in positions which justify the belief that the destructive agent is sewer-gas. The corroding action always takes place from within, and is generally confined to the upper surface of the pipe most frequently in those situations where it lies in an horizontal position, though vertical pipes and the upper surfaces of bends are sometimes affected. Among the diseases he has observed as resulting from this state of things, typhoid fever, diphtheria, scarlet fever, and diarrhoea, are mentioned.
COOLING AND VENTILATION OF RAILWAY-CARRIAGES.
An ingenious contrivance for excluding dust and cooling the air of railway-carriages in hot countries is described in a late number of Engineering. It consists of an arrangement attached to the under side of the carriage, into which air is admitted and made to pass between layers of material that are kept constantly wet by a supply of water from above, and that present a large evaporating surface. By this means all dust is arrested in the chamber, and the air
