Chemistry and Physics. 477 
observation. In the annexed table, column I. gives the name of 
the various lines, column IL their wave-lengths, column III. their 
observed angle of rotation, each being the mean of from six to 
forty-six observations; the last column gives the difference be- 
tween column III. and the value computed by the formula given 
610. E. C. P. 
12. Researches on the Hexatomie Compounds of Cobalt ; by 
Wotcorr Gizss, M.D. 51 pp. 8vo. From the Proceedings of the 
American Academy of Arts and Sciences, vol. xi—The earlier 
the title is given above; notwithstanding its great value, the 
length is so considerable as to make the republication in this 
nitude of this ‘blank, Dr. Tyndall indulges in one or two pre- 
liminary references which, h s, ‘will suffice to show the state 
of the question when this [his] investigation began.’ The first of 
these references cites the opinion of Sir John Herschel to the effect 
‘ason is clear on one point—to wit, than ‘fog is a powerful damper — 
sound,’ 
a & 
the strength of these historical references, Dr 
* . . 
On , Dr. Tynda 
_ ventures the remark that, prior to the investigation conducted by 
