330 Scientific Intelligence. 



observers. As an illustration of the effect of impurity of sub- 

 stance he instances ethyl ether ; distilling this substance over 

 sodium a loss of only 0*7 of one per cent resulted, whereas there 

 was a diminution of five per cent in the value of the latent heat. 

 — Ann. der Physik unci Chemie, No. 7, 1870, pp. 438-449. j. t. 



2. A Mountain Magnetometer. — O. E. Meter has adapted 

 the method of observation employed by Kohlrausch with the 

 variometer to a new instrument. Both the movable needle and 

 the controlling magnet move in a vertical plane instead of in a 

 horizontal one. The instrument is thus a species of dipping- 

 needle or a vertical variometer. The author finds it well adapted 

 to observing the attraction of large masses of rock, and to not- 

 ing changes in the magnetic field in various parts of observatories 

 and laboratories caused by variations in the magnetic condition 

 of the materials of which these buildings are constructed. Ob- 

 servations with this new instrument show that large variations 

 frequently observed in buildings can be attributed as much to 

 change of direction of the magnetic force as to change in total 

 value. The instrument is constructed by W. Siedentopf, Univer- 

 sity Mechanic in Wurzburg. — Ann. der Physik %md Chemie, 

 No. 7, 1890, pp. 489-504. j. t. 



3. Velocity of Transmisison of Electric Disturbances. — Max- 

 well's theory of light demands that the velocity of transmission of 

 electric disturbances along a wire should be equal to the velocity 

 of light through the dielectric surrounding the wire. The velocity 

 is thus determined by the surrounding dielectric in which the 

 energy resides. Professor J. J. Thomson has made a number of 

 experiments upon this subject and finds that the velocity of elec- 

 tric disturbances along wires surrounded by air is 1 '7 times the 

 velocity along the wire surrounded by sulphur. Experiments 

 showed also that the velocities along wires surrounded by air, 

 paraffin and sulphur are approximately proportional to the recip- 

 rocals of the square roots of their specific inductive capacities. 

 The velocity of propagation of a rapidly alternating current along 

 an electrolyte surrounded by air was found not to differ much 

 from the rate along a wire. Experiments with a vacuum tube 

 fifty feet long and a revolving mirror showed that the velocity 

 of discharge through the rarefied gas was comparable with the 

 velocity of light. The experiments on the rate of propagation of 

 electric disturbances lead one to regard the conductor as merely 

 guiding the discharge, " the correlation between the ether and the 

 conductor compelling the discharge to travel along the latter with 

 the velocity of light." Professor Thomson then discusses the 

 application of his observations to the theory of electric striae in 

 vacuum tubes. — Phil. Mag., Aug. 1890, pp. 129-140. j. t. 



4. Phosphor v-photographs of the ultra red. — E. Lommel has 

 taken up anew the method of Becquerel of observing the solar 

 spectrum in the ultra red by means of phosphorescent substances. 

 The spectrum is received on a surface covered with Balmain's 

 paint. A dry photographic plate is then laid upon the phosphor- 



