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frequencies as well as of frequencies measured in millions per second. The Duddell and the Irwin oscillographs, the Vibration galvanometer, and the various types of thermo-ammeters are noteworthy examples of this development.

The application of electrical methods to the measurement of temperature has provided apparatus of unique accuracy and range for the laboratory, the workshop, or the furnace, from the precision resistance instrument with an accuracy of 0’001° C. to the many types of direct reading thermometers, the indicating parts of which may, if necessary, be placed at a great distance from the part which is subjected to the temperature which is being measured. For the highest temperatures there is exhibited by the Cambridge Scientific Instrument Co. the Fery pyrometer, which depends solely on the radiation of heat from the furnace. In the modification of this pyrometer a direct reading instrument is provided without the employment of any electrical apparatus.

The Einthoven galvanometer, shown by the Cambridge Scientific Instrument Co., and the unipivot instruments of Messrs. Paul are interesting developments of modern instruments. The latter provide a series of galvanometers of a sensitiveness hitherto unknown in instruments of a portable design. They are of especial use as temperature indicators, even for ordinary atmospheric temperatures, in conjunction with thermo-couples, which may often be of quite inexpensive materials. The Einthoven galvanometer as an instrument for use in cardiac diagnosis promises to have a future the importance of which it is impossible to estimate.

Among general electrical apparatus, the growing use of decade forms of resistance boxes with rotating contacts superseding those of the plug form, affords a much more convenient apparatus for general work. The employment of mercury contacts, as used in resistances of the highest accuracy, has been adopted in the resistances for the Callendar-Griffiths Wheatstone Bridges employed for precision platinum thermometer work. Among other exhibits of the Cambridge Scientific Instrument Co., the Cambridge extensometer, the cup micrometer, and the rocking microtome are instances of accuracy obtainable in instruments which are notable for their simplicity of mechanical design.

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