103 



crystal will suffer total reflexion at the second surface, while 

 the new kind of vibration is propagated into the air without. 

 The refracted wave will then be always perpendicular to 

 the axis of x' ; the two reflected rays, within the crystal, 

 will be plane-polarized, according to the common law, but 

 they will each undergo a change of phase ; and the vis 

 viva of the two rays together will be equal to that of the 

 incident ray, the vis viva being measured by the square 

 of the amplitude multiplied by the proportional mass. 



In conclusion, the author states a mathematical hy- 

 pothesis by which both the laws of dispersion, and those of the 

 elliptic polarization of rock crystal, may be connected with 

 the laws already developed. 



The Rev. Dr. Todd communicated the following particu- 

 lars concerning an ancient inkstand, contained in a letter from 

 Joseph H. Monck Mason, Esq., dated Rome, May 4th, 1841 : 



" This relic (described by Mrs. Hamilton Gray, in her 

 Tour in Etruria, p. 334) is of coarse terra-cotta, black and 

 ill-formed ; it is a truncated cone, about eight inches long, 

 about four or five inches round the mouth, and about twelve 

 (not more, I think) round the base ; there are about twelve 

 lines of letters written round the upper three-fourths, and 

 one round the very base ; they are written from left to right. 

 I repeat it, that, being cramped by the rules and restrictions, 

 I was not entirely particular ; and the upper part was dirty, 

 and not very legible without close inspection. I could see 

 of the last line (I do not mean that round the base, which has 

 some Greek capitals,) about three-fifths ; this contained four- 

 teen letters. I saw no omicron or omega. This line might 

 have had twenty-four letters ; and allowing about twelve, or 

 say fifteen lines in all, gradually diminishing as on the out- 

 side of a cone, there was scarcely room for ha, be, in a se- 

 cond language. I believe them all to be Greek. About 

 three or four lines up, I remember, there was P {ro,) and 



k2 



