Chemistry and Physics. 413 



following the law of sines. Such a filament of motion is supposed to 

 correspond to a ray of light. The sensation of light is due to the trans- 

 verse vibrations. In a ray of common light the transverse motion is in 

 planes passing through the axis of the ray, and is alike in all directions 

 from the axis ; in a plane-polarized ray, the transverse motion is in 

 planes not passing through the axis ; and in an elliptically polarized ray, 

 the transverse vibrations are elliptical. Prof. Challis has extended his 

 theory to the phenomena of double refraction, by a method which in- 

 volves a new theory of the dispersion of light. He finds the surface 

 of elasticity to be that of an ellipsoid ; which is not in accordance with 

 FresnePs theory of double refraction. The equation of the wave-sur- 



face is, however, the same as in FresnePs theory. 



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traction; by Sir W. S. Harris, (Proc. Brit. Assoc, 1847, Athen., No. 

 1029.)— The author commenced by a brief account of the theory of 

 electricity resorted to by the French philosophers, and then proceeded 

 to notice some physical facts which appeared to invalidate this theory ; 

 —amongst others, the electrical condition of a well-insulated body in 

 a space nearly void of resistance, and which if preserved at a consider- 

 able distance from conducting matter maintained a charge, as well as 

 under ordinary circumstances. The author, by a careful process, had 

 been enabled to preserve the electricity of a small sphere in an ex- 

 hausted medium for a very considerable time — many days. In con- 

 veying a charge to a common electrical jar it might be proved that 

 equal quantities were received into it, in equal times, until there was a 

 sort of overflow; being more analogous to the filling a vessel with an 

 unelastic fluid such as°water, than the condensation of an elastic fluid 

 such as air. The action of the proof plane and the balance of torsion, 

 as employed by the celebrated philosopher, Coulomb, was next advert- 

 ed to. Here the author endeavored to show that great difficulties arose 

 in deducing accurate results, inasmuch as the proof plane could not be 

 considered°as an element of the surface, and any electrometer acting 

 on the principle of repulsion was liable to great uncertainty, and that 

 hence deductions as to the particular distribution of electricity on the 

 surfaces of bodies were inconclusive. It might so happen that the dis- 

 tribution mav be uniform, and yet a proof plane come away more 

 highly charged from one point than from another. 1 he author called 

 attention to an experiment of the celebrated Volta, who found that an 

 electrical charge reposed more quietly on a long rectangular paralle o- 

 gram than on a square, although the areas of the surface were the 

 s ame. It was to be regretted, on account of the received mathe- 

 matical theory of electricity, that all our experimental evidence rela- 

 te to the distribution of a charge on the surface of conductors rests 

 'ipon experiments with the proof plane, or some other body orougnt 

 •nto contact with the given conductor and subsequently removed irom 

 il - The author, by a new method of experiment, had shown that the 

 intensity of a charged surface of any rectangle was the same as when 

 foiled u'p into the form of a cylinder, the quantity of electricity being 

 the same— and that the intensity of a circular area was the same as 

 that of the sphere into which we might conceive it to be transformed. 

 An electrometer, depending on the attractive forces exerted between a 



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