370 POLARISATION. 



The ellipsoid of elasticity to which our results refer has a differ- 

 ent position from that usually assumed, when the axes are similarly 

 directed. With reference to this, it is an ellipsoid rotated to 90, 

 or a reciprocal ellipsoid, since its minor axis takes the position of 

 the major according to the usual representation, and conversely 

 (cf. on this point pp. 322-3). 



A. Cylindrical Objects. 



* A tangential axis is parallel to the axis of the cylinder. 



Caulcrpa prolifera Lamourx. Stem. Trans v. sect, t, long. sect, t, 

 surface doubtful, in the same piece of membrane agreeing with 

 position t, in other places p. Hence, major axis radial. According 

 to action on rotation, biaxially positive. 



Ckamasdoris anmdata Mont. Transv. sect, p, long. sect, p, sur- 

 face p. Hence, major axis longitudinal, minor radial, mean cross- 

 tangential. Probably optically negative ; on account of unevenness 

 of surface of membranes not observed with certainty. 



Acelabidaria mediterranea Lamom^x. Stalk. Action similar to 

 Chamcedoris annulata. 



Valonia jEyagrapila Ay. Transv. sect, p, long, sect.p, surface t. 

 Hence, major axis cross-tangential, minor radial, mean longitu- 

 dinal. Optically positive ; angle of optic axes about 80. 



* The tangential axes stand acutely to the axis of the cylinder. 



Stachys spec. Thin-walled hairs of the stalk. Produce neutral 

 longitudinal stripes near the margin. The orthogonal position = 

 appears to be consecutive, the position at right angles to it |j 

 alternative; consequently left-handed rotation. Angle 0, after 

 measurements in split hairs, about 17; left-handed rotation 

 confirmed. In agreement with the above we get transv. sect, t, 

 margin /, surface p. Hence, minor axis transverse to the left- 

 handed spiral ; the ratio of two other axes unknown. 



Trifolium rubens L. Thick- walled hairs of calyx of fruit. 

 Action similar to hairs of Stachys ; with neutral longitudinal 

 stripes and left-handed rotation ; angle < unknown. 



Abies excelsa DC. Old wood, macerated in nitric acid and 

 chlorate of potash, (a.) Thin-walled wood-cells. Transv. sect, p, 

 margin p, surface p. Position = appears to be consecutive, 



