NATURAL PHILOSOPHY. 183 



welded together, from the heat generated by friction, probably 

 from a lack of lubrication. 



Temperature of Regelation. — Prof. Edward Hiingerford, of Bur- 

 lington, Vermont, at the 1868 meeting of the American Associa- 

 tion, gave an account of some experiments on snow and ice at a 

 temperature of below 32° F. The main point was to show that it 

 is not necessary for the reunion of broken ice and snow into a 

 compact mass that any portion of the mass should attain a tem- 

 perature above the freezing-point. He thought, from his experi- 

 ments, that the theory of Professors Tyndall and Forbes of regela- 

 tion is not correct, and is not necessary to e;splain the movement 

 of glaciers. He thought, also, that the snow at the summits of 

 mountains might be converted by pressure into glacier ice at tem- 

 peratures far below the freezing-point of water. 



Eff'ect of Surface on Radiation. — The following experiment was 

 made recently, by Mr. Balfour Stewart, at the Royal Institution. 

 A cannon-ball with chalk-marks upon it, and a tile with a white 

 and black pattern, were heated to redness and viewed in a darkened 

 room. It was found that the black parts of both objects emitted 

 more light than the white ones. 



Trees vs. Evaporation. — Trees should not be cut away from the 

 borders of ponds, as they protect the water from evaporation. In 

 the summer of 1864 a calculation was made, wdiich showed that 

 in 40 days the evaporation of an unprotected pond, containing 

 about 14,000 gallons of water, was 9,000 gallons ; as much, in 

 fact, as would have supplied a flock of 500 sheep for the time. 



Beat Generated by Magnetism. — If a magnet, its poles pointed 

 upward, be made to revolve rapidly in a vertical axis below a 

 small copper plate, on w4iich is placed a glass flask, the tempera- 

 ture in the flask is sensibly increased ; it is believed, that in a 

 copper vessel containing water sufficient heat may be generated 

 by the rapid rotation of the magnet to make the water boil. 



On the Electric Conductivity of Platinum, as affected by the Process 

 of Manufacture. — Mr. C. W. Siemens gave in a paper before the 

 British Association, in 1868, the results of experiments which hac 

 been made in fusing and condensing platinum, from which it ap 

 peared that platinum, which had been obtained by fusion, diifered 

 from platinum w hieh had been obtained by condensation ; that 

 between platinum at 80° and platinum at 100°, the variation 

 was in the one case 26 per cent., and in the other, 28 per cent., 

 and that in dealing with platinum it was necessary to discriminate 

 very carefully between condensed and fused. 



Perforation of Glass by the Electric Spark. — Mr. E. S. Ritchie 

 exhibited before the Massachusetts Institute of Technology, an 

 inch cube of clear glass, which had been perforated by the Rhum- 

 korff" electric spark, which he has succeeded in obtaining of a 

 length of 14 inches. He can perforate in this way glass If 

 inches tliiek, but the apparatus must be arranged in a peculiar 

 manner, or the spark will go over instead of through the glass. 

 The spark will not go through twice in the same place, but make 

 a new passage each time. 



Electrical Experiment. — M. Becquerel, in making some re- 



