Nor do I propose to make these Lectures in any sense exhaustive, but, on the contrary, to include in them only such information as is essential, and such as you may readily, and without effort, retain in your memory. I shall direct especial attention to practical points which are of importance to the successful use of electricity; for from non-observance of small details of application many failures have resulted, the treatment getting a measure of discredit, which in _strict justice_ should have attached only to the operator. In the present Lecture I shall consider instruments, their construction and management, a dry subject, but an essential one, the first requisite of a good workman being complete familiarity with his tools, lacking which he will be the victim of constantly recurring annoyances and difficulties; for although the present position of electro-therapeutics is largely due to improved methods of administration, these methods would be impossible with faulty instruments, while, on the other hand, the most perfect instruments require a certain amount of skill and care in their management, and some acquaintance with at least the mechanical details of their construction; and without this rudimentary knowledge it is also impossible to usefully compare one instrument with another.[4] My second Lecture will be devoted to the different methods of applying electricity, and my third and last to its uses in the diagnosis and treatment of disease. [SN: Varieties of Electricity.] We make use of three varieties of electricity in medicine. Firstly, of static or friction electricity, the electricity of glass and amber, appropriately called from its early investigator, _Franklinism_. Secondly, of the electricity of chemical action, _Galvanism_, or better, _Voltaism_, the “_Constant Current_.” Thirdly, of _Faradism_, the induced currents of momentary duration, which are generated or _induced_, in a coil of wire by the action upon it, under certain circumstances, of a magnet, or of a Voltaic current. FRANKLINISM. Franklinism, sometimes of the utmost value, and far surpassing, in certain cases, any other form of electricity, has some inconveniences in its application, and has hitherto been little used but by specialists. Recent improvements in Franklinic instruments have, however, largely removed these inconveniences, and have placed at the general service of the profession a remedy of much good and still greater promise. The fundamental requisite in all Franklinic machines, consists in the rotation of a glass plate against a leathern or other rubber, and the accumulation of the resulting electricity upon a metallic receiver, insulated by a non-conducting support, usually of glass. [SN: Franklinism]