TRANSACTIONS OF THE SECTIONS. 11 



oppositely polarized pencils, which produce by interference all the colours exhibited 

 by such crystals under similar circumstances. 



2. The two oppositely polarized pencils are, first, the pencil polarized by refraction 

 at each surface ; and secondly, the pencil, or rather the fasciculus of pencils reflected 

 from the surfaces of each film, and returned into the transmitted beam. 



As these phenomena are exactly the same as those produced by double refraction, 

 the author did not hesitate to call the result a new species of double refraction, or a 

 new process in which the phenomena of double refraction are produced. 



On the Decomposed Glass found at Nineveh and other places. 

 By Sir David Brewster, K.H., LL.D., F.R.S. 



The author described the general appearance of glass in an extreme state of decom- 

 position, when the decomposed part was so rotten as to break easily between the 

 ringers, a piece of undecomposed glass being generally found in the middle of the plate. 

 He then explained how, in other specimens, the decomposition took place around one, 

 two, or more points, forming hemispherical cups, which exhibit the black cross and 

 the tints of polarized light produced by the interference of the reflected with the 

 transmitted pencils. In illustration of this decomposition, he showed to the Meeting 

 three specimens, in one of which there was no colour, but which consisted of innu- 

 merable circular cavities with the black cross, these cavities giving it the appearance 

 of ground-glass. In another specimen the film was specular and of great beauty, 

 showing the complementary colours by reflected and transmitted light. In a third 

 variety the films were filled with circular cavities exhibiting the most beautiful colours, 

 both in common and polarized light. Various other remarkable properties of these 

 films were described by the author. 



On the Submergence of Telegraph Cables. By H. Cox. 



On the Stratified Electrical Discharge, as affected by a Moveable Glass Ball. 



By J. P. Gassiot, F.B.S. 



If the discharges from an induction coil, when taken in a good carbonic acid va- 

 cuum tube, are examined with care, it will be seen that the stratifications nearer the 

 negative terminal are remarkably clear and defined, oftentimes showing clearly sepa- 

 rated cloud-like luminosities, but gradually becoming indistinct and intermingled with 

 each other towards the positive terminal wire. This difference in the character of the 

 stratified discharge becomes more perceptible to a certain extent as the vacuum im- 

 proves ; for when the stratifications are close and narrow, they are regularly diffused 

 throughout the entire length of the luminous discharge. 



In a tube 18 inches long and \\ inch wide, I inserted a small bead of uranium glass 

 about \ of an inch in diameter. Transparent uranium glass, Professor Stokes has 

 shown has the property of becoming opake by the electric light, and this is very beau. 

 tifully shown in these tubes, but more particularly when the negative discharge is 

 made to impinge on the bead. If during the discharges the tube is inclined so as to 

 permit the bead to roll down, the discharges will give the appearance as if a distinct 

 row of separated beads were present ; this appearance arises from the number of dis- 

 charges which take place during the rotation, each discharge separately and distinctly 

 illuminating the bead. 



The peculiar phenomenon which I, however, desire to bring before the notice of the 

 Section is one which I only very recently noticed. I have already stated that the 

 stratifications near the positive wire are indistinct ; but if the glass bead is placed 

 near the positive wire and then allowed slowly to descend towards the negative, the 

 stratifications at the positive are at first as clearly defined near that terminal as at the 

 negative, and as the b^ad rolls gently down, they have the appearance of following 

 the bead and issuing one after the other from the positive wire, until the bead reaches 

 to within a few inches of the negative, when this action gradually ceases. If the tube 

 is now inclined so as to allow the glass bead to return in the contrary direction, the 

 stratifications appear to recede, becoming more and more clearly defined, until the 

 bead passes the positive terminal wire, when the entire discharge returns to its norma* 

 state. 



