for the Advancement of Raience 393 
the violet rays (as in so many other oils) was rch’ as to render the line | 
H very, ind iinet its index ts therefore marked*agdoubt fal. — 
: aes for the the Standard rd Raya 
or > 
ase a — 1:4899 | “14868 
15034} 1 sone 15091 
167 | 5151 rs 525 
5. 20 ides Cai 14641 ts 14658 SE 14728 
ie my report ers I stated the impossibility of obibinin measur 
yo gd of lead from the absence ofall appearance of lines,an 
entire absorption of the blue and violet: portion of the spectrum. E 
ine eoroent that in the absence of any determin ations” ‘of the kind it Be 
t-not be-useless to give the very rough estimates: which my former Se 
soliscipia enable me to obtain by means of the ta of blue glass, — 
which gave a poi et to D, and 
; exire fy reen space visible might be about e most refracte 
Of the two spectra (given by the double acts ee the mibatniis) 
“was the: ent. defined, and in this the oh corresponding to D is ex- 
tremely uncertain. The mean of two sets of observation was as fol; 
lows :—Prism of chroinate of Yaad: axis of prism. perpendicular to Q axis - 
of crystal, mean atigle guajeed by: ‘reflexion and_ a) measurement - es 
ist mao ; -. 2nd Sp ven 
af. Ray. A pee leas 
_ | * >. Extreme red, eet 
about B 229 | 858. 26° 30’ 2°84 
about D 23° 10! 2°55 29°? 300? 
about E 24° 30/ 2°70 30° 30° 310 
While upon the subject, I may be allowed to remark, that. as attempts 
are now making, with so much promise, for procuring optical glass 
superior quality, it would be highly snteaaiind if specimens were cut 
Into prisms (portions of half an inch cube, or even less, will a and 
two sides only need be polished, containing an angle o 
in Fraunhofer’ s glass nearly six hundred were Tibi 
On the Magneto-optic Properties of Crystals, and the Relation of 
etism and Diamagnetism to con gi Arrangement ; by 
Messrs. J. Pepsacs and Hermann sein ka0 
During the joint net carried on more aa one hundred natural 
had been examined. The results were thus briefly summed 
_ Seconp Serres, aah X, No. 30.—Nov., 1850, 0 
