*A 



V '* '^ 



112 Scientific Intelligence. 



The turpentine No. 1, was pure and had been rectified in a current 

 of steam, its rotation was towards the right; No. 2, was another va- 

 riety which had not been rectified and turned the plane of polarization 

 to the left; the oil of lemon was also pure and distilled like No. 1: 

 the author found that with pure oil of turpentine the observed angles of 

 rotation never differed more than 5' from the mean, whereas with oil 

 of lemons the differences were much greater, the turpentine was there- 

 fore preferred for experiments with the galvanic current. The gal- 

 vanic apparatus employed consisted of two helices of copper wire 

 g.gmm JQ thickness, and weighing each about 6 lbs. ; they were placed 

 with their axes in the same straight line and had together a length of 

 about 9 inches ; in the axis of these coils was placed the tube contain- 

 ing the liquid to be examined. The current from a battery of about 

 30 pairs, (partly Grove's, partly Bunsen's and partly iron-zinc,) was 

 made to pass through a gyrolrope, a tangents-compass, and the whole 

 length of the coils themselves. In this manner the author studied the 

 deflecting action of the current upon the plane of polarization in bisul- 

 phid of carbon and in oil of turpentine ; the result of his Investigation 

 he gives in the follow^ing statements. 



(1.) The law of Biot, according to which- the rotation of the plane 

 of polarization of any color is inversely proportional to the square of 

 its wave length does not hold good for oil of turpentine or oil of lemon, 

 any more than for rock-crystal, (as shown by Bloch.) 



(2.) The law of Faraday, according to which the deflection of the 

 plane of polarization is proportional to the intensity of the deflecting 

 current, holds good for those substances, which in themselves deflect 

 the plane of polarization, as well as for those which do not do so. 



(3.) The deflection of the plane of polarization of different colors 

 by the galvanic current is in the case of rotating as well as not-rotating 

 substances, greater in proportion as the wave length of the color in 

 question is less. In rotating substances like oil of terpentine, this 

 deflection is proportional to the deflection produced by the substance 

 itself upon the plane of polarization of each particular co\ox.—Pogg^ 

 Ann., 1851, No, 2. 



2. Physical Demonstration of the Rotation of the Earth ly means 

 of the Pendulum, — Foucault has communicated to the Academy of 

 Sciences an account of %n experiment which has excited universal 

 attention and interest, and which has since been frequently repeated 

 with success. The experiment consists simply in suspending a heavy 

 ball to a long and flexible string, and allowing the whole to vibrate 

 freely in the manner of a pendulum ; under these circumstances it will 

 be found that the plane of vibration gradually changes its position, 

 turning slowly from east to west. To understand what takes place in 

 this case, it is necessary to consider first the experiment as made at 

 the pole, and the pendulum as suspended from a point in the axis of iho 



earth prolonged and independent of the motion of the earth itself; it is 

 evident that in this case, as the earth moves from west to east the plane 

 of vibration of the pendulum which is in reality fixed, will appear to 

 move from east to west. Next suppose the pendulum suspended from 

 a point in ihe axis of the earth prolonged, but attached to and moving 

 with the earth itself, it is evident, and it may easily be demonstrated 



