I am induced to speak thus strongly because men of scientific reputation have advocated the habitual use of the galvanometer, not alone by medical men trained to precision of observation, but by private patients as “_enabling them to carry on the treatment at home with all the accuracy desirable!_” The prospect of the ordinary patient provided with a battery, the use of which he is complicating by a galvanometer, is anything but reassuring to those physicians who not only prescribe electricity, but are themselves habituated in applying it--which, by the way, is a very different thing--and who have had frequent experience of the manner in which patients misunderstand, or fail in correctly carrying out, the most explicit directions. Electricity will be left in the hands of specialists, and necessarily do but a tithe of the good it is capable of affecting, until the mass of the profession can be induced to master the few preliminary details essential to its successful application, and I fear that the suggestions that have been made--suggestions which I believe to be entirely without foundation--that there exist practical difficulties to its dosage, will tend to postpone rather than to accelerate its more extended use. Should any of you desire to use a galvanometer, that patented by Sprague, of Birmingham, is the one most adapted for use in medicine. Electricity is a force, and as with other forces it has its standard of measurement. In mechanics we know that the power sufficient to raise one pound to the height of one foot is the basis of measurement. Similarly in electricity the unit of measurement is the force which will raise one gramme to the height of one metre, and the standard multiple of this was called a “British Association Unit,” or shortly, a “B.A.” unit, and it is now called an “_Ohm_” when used to measure the resistance offered to the current, and a “_Veber_” when used to measure the strength of the current itself. The ordinary galvanometer is founded on the principle that a magnetic compass needle has a tendency to place itself at right angles to a current of electricity, and the degree to which the needle is deflected is a measure of the quantity of electricity, but the angle of deflection is not proportionate to the current strength, and it differs in different galvanometers; but in “Sprague’s Galvanometer” the dial is divided, not into degrees, but into divisions of thousandths of _Vebers_--divisions which were obtained by noting the deflections given by the needle with currents of known strength. I am indebted to Mr. Sprague for his courtesy in endeavouring to so modify his galvanometer as to render it available as a graduator of doses of interrupted Voltaic electricity, but although he has not succeeded in doing this, he has constructed for me an instrument which, supposing that a battery be partially exhausted, will indicate with precision the absolute strength of, say, twelve