i 



i 



r 



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I 



Miscellaneous Intelligence. 445 



2. Gyroscope. — Major Barnard will continue his discussion of the 



gyroscope in the January number of this Journal, and treat especially of 



"the motions of the gyroscope as modified by the retarding forces of 



friction and resistance of the air," — explaining the discrepancies between 



the theoretical motion of a "solid of revolution" without friction or other 



retarding influences and the observed motions oi the experimental i^yro- 

 scope, 



3. Rajyidiiy of thought or nervous action ; by M. Ule, (Revue Suisse, 

 March 16, 1857). The method of transforming the valuation of time 

 into space by the rapid revolution of a cylinder, proposed hy Mr. Fizeau, 

 has been applied fo the measurement of the rapidity of nervous impulse. 

 Such a cylinder rotating ] 000 times a second, and divided into 3G0 

 degrees, may measure l-360j000th part of a second; or rotating 1500 

 times a second, l-540,000th part of a second ; and even this may be 

 subdivided by a microscope, so as to obtain the 10-milliontIi or perhaps 

 lOG-millionth part of a second. By this extreme minuteness of subdivisiou 

 of time, it is not difficult to measure even the rapidity of a nervous im- 

 pulse. If an electric shock be given to the arm, it produces a sensation, 

 and a contraction of the muscles. Hence by noting the interval of time 

 between the shock and the contraction, the time occupied by the trans- 

 mission of the sensation and the action of the brain, however quick, will 

 be determined. By trying the experiment with different parts of the 

 body, sensible differences have been observed, the shock applied to the 

 thumb being one-thirtieth of a second behind that applied to the face; 

 and this diftercnce pertains to the transmission and not to the action of 

 the brain, and hence enables us to eliminate the latter in tlie experiments- 

 In this way it has been found by M. Helmholtz, by whom these experi- 

 ments have been made with the most care, 



(1,) That sensations are transmitted to the brain at a rapidity of about 

 l^Q feet per second^ or at one-fifth the rate of sound; and this is nearly 

 the same in all individuals. 



(2.) 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 the condition at the time, and is 

 more regular, the more sustained the attention. 



(3.) The time required to transmit an order to the muscles by the motor 

 nerves, is nearly the same as tliat 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. 



4.) The whole operation requires 1^ to 2 tenths of a second, 

 onsequently 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. 



4. Smithsonian Conlrilutions to Knowledge, Vol. IX, 4 to.— Contents. 

 L. W. Meech : On the relative Intensity of the Heat and Liglit of the 

 Sun upon different latitudes of the earth. 58 pp., with 6 plates. 



Edw-arc IIiTcncocK: Illustrations of Surface Geology.^ 1C4 pp., with 



12 plates. 

 Braxtz Mater : Observations on Mexican History and Archaeology, 



-^ith a special notice of Zapotec Remains as delineated in Mr. J. S. Saw- 

 kin's drawings of Mitla, etc. 36 pp., with 4 plates. 



