Who but a Frenchman would ever have thought of trying to measure 'the rate at whieh our ideas How ? One has thought of it, and three gentlemen of France have experimented and discoverednot exactly the rate at which our ideas travel, for that is infinitebut the time which elapses between the moment we think of a thing and the moment our muscles are affected to do it ; or, in other words, what time it takes for the brain to exert its influence on the senses, and the senses on the brain. We compile the following information from a French journal :If a cylinder divided into 360 degrees be caused to rotate 1,000 times in a second, it is evident that the passage of one of those degrees before a given point is equal to the 1-360,000th part of a second ; this may be divided by a microscope so that a period of time equaling the ten millionth, or even the one hundred millionth part of a second may be measured. By this arrangement it is possible to measure the rate of nervous impulse. Suppose an electric shock be given to the arm, it produces a sensation and a contraction of the muscles ; then by noting the interval of time between the shock and the contraction, the time occupied by the action of the brain to produce the contraction, howcver quick, will be ascertained. By trying this experiment on various parts of the body, the amount of sensibility of the different leading muscles may be determined. M. Helmholz, a Swiss gentleman, has made some very interesting experiments, with the utmost care, and has arrived at the following re,ults, which we copy from Professor Silliman's American Journal of Science: Sensations are transmitted to the brain at a rapidity of about 180 feet per second, or at one-fifth the rate of sound ; and this is nearly the same in all individuals. The brain requires one-tenth of a second to transmit its orders to the nerves which preside over voluntary motion ; but this amount varies much in different individuals, and in the same individual at different times, according to the disposition or condition at the time, and is more regular, the more sustained the attention. The time required to transmit an order to the muscles by the motor nerves is nearly the same as that required by the nerves of sensation to pass a sensation ; moreover, it passes nearly one-hundredth of a second before the muscles are put in motion. The whole operation requires Ii to 2 tenths of a second. Consequently, when we speak of an active, ardent mind, or of one that is slow, cold or apathetic, it is not a mere figure of rhetoric, but an absolute and certain fact that such a distinction, with varying gradations, really exists.