1893.] Eocpe7'iments on the Reflection of Light. 81 



the effect of electrostatic force upon an isotropic transparent 

 medium is to ccmvert it into one which is optically equivalent 

 to a uniaxal crystal, whose axis is parallel to the direction of 

 the force. Under these circumstances it would appear probable 

 that a strongly charged metallic conductor would behave like 

 a doubly refracting metallic medium, having a single optic axis 

 whose direction is normal to the surface of the reflector. If this 

 conjecture should turn out to be correct, we should anticipate 

 that when polarized light is reflected, the component vibration 

 in the plane of incidence would be much more affected than the 

 component perpendicular to that plane ; and that the values of 

 the principal incidence and azimuth and also the differences be- 

 tween the changes of phase of the two components would also 

 be affected by electrostatic action. No experiments upon reflection 

 from electrified metallic reflectors appear as yet to have been 

 made ; but I am strongly inclined to think that such experiments 

 would repay the trouble involved in making them, and would 

 reveal some entirely novel and interesting phenomena. 



Monday, May 15, 1893. 



Prof. T. M^K. Hughes, President, in the Chair. 



The following Communications were made to the Society: 



(1) Exhibition of abnormal forms of Spirifera lineata {Martin) 

 from the Carboniferous Limestone. By F. R. Cowper Reed, B.A., 

 Trinity College. 



This species, as defined by Davidson, is normally subject to 

 great variation of form and ornamentation, as it includes 8p. im- 

 bricata and Sp. elliptica. Specimens with intermediate characters 

 are however common. The series of abnormal forms exhibited 

 showed the gradual development of a sharp median groove both 

 in the dorsal and ventral valves so as ultimately to produce a 

 bilobed shell. From the nature of these grooves interruption of 

 the shell-secreting action of the mantle seems to have occurred 

 along a definite line : and the cause may have been disease, the 

 presence of a parasite or foreign body, or pressure during Iffe. 

 Similar malformation is seen in some Terebratulas, etc. The 

 normal and regular bilobation of some species of Orthis, Terebra- 

 tula, etc., is comparable. 



(2) Exhibition of Post-Glacial Mammalian bones from Bar- 

 rington recently acquired by the Museum of Zoology. By S. F. 

 Harmer, M.A., King's College. 



(3) Exhibition of a specimen shewing Karyokinetic division of 

 the nuclei in a plasmodium of one of the Mycetozoa. By J. J. 

 Lister, M.A., St John's College. 



