218 Scientific Intelligence. 



distance. Such attraction would be caused by granular media in 

 virtue of this dilatancy and stress. More than this, when two 

 bodies in a granular medium under stress are near together the 

 effect of dilatancy is to cause forces between the bodies in very 

 striking accordance with those necessary to explain coherence of 

 matter. So far as the integrations have been carried, it appears 

 with a certain arrangement of large and small grains that the 

 forces between the bodies would be proportional to the product 

 of the volumes divided by the square of the distance; i. e., that 

 the state of stress of the medium may be the same as Maxwell 

 has shown must exist in the ether to account for gravity. — Phil. 

 Mag., V, xx, 469, Dec, 1885. G. r. b. 



2. On the use of the Induction Spark in Spectrum work. — In 

 noticing Lagarde's research on the hydrogen spectrum, E. Wiede- 

 mann has criticised the results obtained, since the induction spark 

 was used as a source of electricity. Hence the numerical values 

 given in his paper have no exact significance and furnish only a 

 general idea of the phenomena. It is a well known fact that the 

 discharge of an induction coil is a complex phenomenon, the pri- 

 mary discharge being followed by a series of partial discharges 

 with decreasing intensity. Hence if the induction spark be used 

 to produce spectra, the intensity and character of these spectra 

 change with each partial discharge, one of these discharges pro- 

 ducing perhaps a line spectrum while another gives rise to a band 

 spectrum. But the effect upon the eye is even more complex. It 

 is not the sum of the impressions which is observed, since the dimi- 

 nution of visual sensitiveness with time is felt in a very different 

 manner when the discbarges are of different intensities. It is true 

 that the Holtz machine is not so ready a means of supplying the 

 spark as the induction coil. But that difficulty is more than coun- 

 terbalanced by the accuracy of the results obtained with it. To 

 prove that in Lagarde's method there were partial discharges to a 

 marked degree added to the principal one, the author constructed 

 a tube of the same dimensions as that used by him, and examined 

 the character of the induction spark within it by means of a revolv- 

 ing mirror. In place of seeing a single line, a long luminous band 

 was visible corresponding to a great number of partial discharges. 

 — Ann. Chim. P/iys., VI, vii, 143, Jan., 1886. &. p. b. 



3. On the Vapor-pressures of Mercury. — The great importance 

 of an accurate determination of the pressures of mercury vapor 

 at different temperatures, and the fact that the values given by 

 Regnault and hitherto relied upon, are regarded by him as only 

 approximations, has led Ramsay and Youmg to experiment in 

 this direction with an improved apparatus. It consisted of a 

 U-tube connected with a manometer and enclosed in a jacket 

 containing the substance whose boiling point gave the tempera- 

 ture. The U-tube was filled with mercury and boiled to expel 

 air. On heating it and diminishing the pressure by means of 

 a pump, vapor was evolved from the mercury depressing the 

 level on one side and raising it on the other. From the differ- 



