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 chronograph corresponding to the big wave made by my hand. You see we have twenty little waves. Thus twenty hundredths, or one-fifth of a second, represents the time occupied by the rapid movement of my hand.

It is impossible, in a lecture-theatre like this, to show to a large audience, such as I have the honour to address, the curves described by any recording apparatus on a rotating drum or cylinder. What we need is an arrangement by which the curves can be at once projected on a screen by the electric light. Indicating my wants to Mr. Horace Darwin, of the Cambridge Scientific Instrument Company, we have been able to devise the apparatus now before you, and which we will call the R. I. Railway. As it will be used chiefly for obtaining the curves of contracting muscles, it may well be named the railway myograph. You see it is a triangular frame, carrying a large plate of glass secured in a vertical position. The glass is blackened with soot in a smoky flame, and, of course, the soot prevents any light from passing through it; but if any soot is rubbed off, as when we draw a line on the plate with the point of the pencil, the light shines through,