Page:Popular Science Monthly Volume 4.djvu/333

Rh reached, so that the professor states that "the duration of the first act of the electrical discharge is in certain cases only forty billionths of a second, an interval of time just sufficient to enable a ray of light to travel over forty feet." The duration was twenty-five times smaller than had ever before been measured. In this infinitesimal portion of time a strong and distinct impression upon the retina is made, so that "the letters on a printed page are plainly to be seen; also, if a polariscope be used, the cross and rings around the axis of crystals can be observed with all their peculiarities." Nor is this all; "as the obliteration of the micrometric lines could only take place from the circumstance that the retina retains and combines a whole series of impressions whose joint duration is forty billionths of a second, it follows that a much smaller interval of time will suffice for vision. If we limit the number of views of the lines presented to the eye in a single case to ten, it would result that four billionths of a second is sufficient for human vision."

We saw at the outset how much an act of vision involves, and we have now some idea of how long it takes. If the discharge of the thunder-cloud occupies, as was stated, the one five-hundredth of a second, the "interviews" of our philosopher with the "amber-spirit" were at least fifty thousand times "quicker than lightning."



R. SPENCER recently called the attention, in a very interesting passage of his "Psychology," to those secondary signs of a feeling which are to be found in abortive attempts to conceal it. "A state of mauvaise honte" he well says, "otherwise tolerably well concealed, is indicated by an obvious difficulty in finding fit positions for the hands." A great mental agitation, though prevented from breaking out into violent expression, is pretty certain to betray itself in the awkward, shuffling movements which are made to curb and suppress it. Such indirect signs of emotion Mr. Spencer calls its secondary natural language.

The fact that many of our emotions now betray themselves only through the incompleteness of the effort of will to disguise them is not a little curious, and offers several lines of interesting inquiry. It at once suggests how very little play for emotional expression the conditions of modern society appear to allow. For it seems tolerably certain that the voluntary hiding of feeling is a late attainment in human development, and is forced on us simply by the needs of advancing civilization. Savages, for the most part, know little of concealing their passions, and this makes them so good a psychological 