May, I92I. ] STATIC IN RAOI0 TELEGRAPHY. 629

of the forenoon, and that the directivity frequently becomes more pronounced as the static becomes more severe.

8. Two types of static in respect to tuning have been noted in our laboratory, one giving a pure shock effect is heard simultane- ously over a wide range of wave lengths, and one in which the crashes are not heard simultaneously at different wave lengths. This last we have called the spectrum type, since it appears to consist of a large number of independent waves of different lengths forming a continuous static spectrum. There is some reason to believe that the spectrum type forms a large part of the directive static.

9- At present it is impossible to formulate any completely satisfactory theory of the origin of static, but it appears probable that it originates in the upper atmosphere in powerful discharges between air bodies at different potentials, ~ though it is difficult to understand how such discharges which give rise to electrical waves more powerful than those from the largest radio station, can take place without luminous phenomena. I f the disturbing waves are formed in this way in the upper atmosphere, the wave front un- doubtedly spreads out until it reaches the earth, where it grounds itself exactly like the radio waves from an aeroplane and then moves off with a practically vertical wave front as if it had come from an antenna on the earth's surface.

The results of the observations thus far made, f ragmentary as they are, indicate plainly the importance of taking static direc- tional observations wherever radio stations are situated, and war- rant plans for a general static survey which shall extend eventu- ally to all parts of the world.

On the Resistance of Copper Sulphate in Glycerine. A. GIL- 5{ouR. (Phil. May., March, I92I. ) When a high resistance is needed that has small capacity it is found that a solution of copper sulphate in glycerine answers well. Such solutions are quite free from polarization. They are, however, hygroscopic and should be sealed to avoid contact with the air. Tables are given of the specific resistance of solutions of different concentrations.

An interesting obiter dictum is, " Glycerine has been known for a long time as a solvent of very wide range--at least as ex.tensive as that of water."

G.F.S.

2 See Pickard's article cited.