Page:Popular Science Monthly Volume 25.djvu/755

Rh, whether of the chest as a whole, or of the portion over the heart, it sucks in or blows out a little puff of air. A thin India-rubber tube connects its nozzle with a flat elastic bag under the short arm of a lever. The other end of the lever moves up and down in accordance with the part of the chest to which the pneumo-cardiograph is applied, and scratches light marks on a band of paper which is driven onward by clock-work. This little instrument can be worn under the buttoned coat without being noticed. I was anxious to practice myself in its use, and wore one during the formidable ordeal of delivering the Rede Lecture in the senate-house at Cambridge, a month ago (most of this very memoir forming part of that lecture). I had no connection established between my instrument and any recording apparatus, but wore it merely to see whether or not it proved in any way irksome. If I had had a table in front of me, with the recording apparatus stowed out of sight below, and an expert assistant near at hand to turn a stop-cock at appropriate moments, he could have obtained samples of my heart's action without causing me any embarrassment whatever. I should have forgotten all about the apparatus while I was speaking.

Instrumental observers of the reflex signs of emotion have other means available besides this, and the sphygmograph that measures the pulse. Every twitch of each separate finger even of an infant's hand is registered by Dr. Warner's ingenious little gauntlet. Every movement of each limb of man or horse is recorded by Dr. Maret. The apparatus of Mosso measures the degree in which the blood leaving the extremities rushes to the heart and head and internal organs. Every limb shrinks sensibly in volume from this withdrawal of the blood, and the shrinkage of any one of them, say the right arm, is measured by the fall of water in a gauge that communicates with a long bottleful of water, through the neck of which the arm has been thrust, and in which it is softly but effectually plugged.

I should not be surprised if the remarkable success of many persons in "muscle-reading" should open out a wide field for delicate instrumental investigations. The poetical metaphors of ordinary language suggest many possibilities of measurement. Thus, when two persons have an "inclination" to one another, they visibly incline or slope together when sitting side by side, as at a dinner-table, and they then throw the stress of their weights on the near legs of their chairs. It does not require much ingenuity to arrange a pressure-gauge with an index and dial to indicate changes in stress, but it is difficult to devise an arrangement that shall fulfill the threefold condition of being effective, not attracting notice, and being applicable to ordinary furniture. I made some rude experiments, but, being busy with other matters, have not carried them on, as I had hoped.

Another conspicuous way in which one person differs from another is in temper. Some men are easily provoked, others remain cheerful even when affairs go very contrary to their liking. We all know