electrometer gives as much as 100 divisions on the scale for one single cell of the battery. In Mr. Varley's patent of 1860, he describes a method which he employed to make the one plate charge itself, and on this principle he constructed a large electrical machine, which he exhibited at a soiree of the Royal Society of 1869-70. This machine has been adopted by Sir William Thomson for maintaining the charge in his electrometer. The new electrometer is really a combination of three inventions--of Sir William Thomson's portable electrometer to indicate whether or no the instrument is sufficiently charged; of the replenisher by Mr. Varley for charging or discharging; and of the quadrant electrometer for reading off the minute tensions measured. The instrument is in its present form so practically useful that it has been largely used in connection with telegraphic cables, and Mr. Varley has calculated tables to enable any electrician at a glance to infer from two readings by this electrometer the insulating power of any telegraphic cable. Sir William Thomson is no specialist. Many people are accustomed to associate his name with the Atlantic Cable, and with that alone. This, however, is a great mistake, for he has made many important additions to the science of magnetism, respecting which he published a number of valuable papers between the years 1847 and 1851. He has also displayed extraordinary acumen and intelligence in the investigation of the nature of heat. Neither should it be forgotten that Sir William has speculated a great deal on the ultimate constitution of matter--an inquiry which has occupied the attention of all great physicists in modern times. Last year he published in _Nature_ an article which, running from four different lines of argument, seeks to establish proof of the absolute magnitude of the atoms of matter. Of this argument Tyndall says:--"William Thomson tries to place the ultimate particles of matter between his compass points, and to apply to them a scale of millimetres."