Page:Popular Science Monthly Volume 6.djvu/405

Rh

 The upper line of figures numbers the seconds; and as twenty of them are shown, and the cylinder revolves once every sixty seconds, about one-third of the length of the strip of papaer is here represented. The middle column of figures numbers the lines, and, therefore, the minutes. The jogs in the lines are represented so exactly at intervals of one second as to give the effect of columns across the paper. As explained in the text, it is all done by one pen, which makes one continuous line round and round, the machine making regular jogs as a time-scale, and the observer making the regular jogs at the instant the star reaches the thread; its time being thus exactly recorded.—[Ed.