Spectral Investigations. 205 Registering Electrometer.'The quantities of atmospheric electricity and terrestrial magnetism are so minute that they have hitherto been measured by delicate apparatus and rccorded by photography, a process which is very costly and often unsatisfactory. Mascart has invented a mechanical register, to accompany Sir Wm. Thomson's electrometer, which gives admirable results. It can be connected with various other iustrumcnts.--La Nature. C.