Physics. 265 
to suspect that the meyiies of the neutral point was not Sonnets 
but that it varied with the density of the illuminated fum 
The examination of these questions led to the falloneoae aie and 
fumes of incense, ood. sufficient time being allowed for their uni- 
form diffusion, the electric beam was sent through the smoke. 
eam. 
neutral point, with complementary effects at opposite sides of 
it, was also exhibited by the beam. The angle enclosed by the 
axis of the beam, and a line drawn from the neutral point to the 
observer’s eye, measured in the first instance 66°. 
he windows of the laboratory were now opened for some min- 
utes, a portion of the incense” smoke being permitted to escape. 
On again darkening the room and turning on the beam, the line of 
vision to the neutral pont was found to enclose with the axis of 
the ee an angle of 6 
windows were vit opened for a few minutes, more of the 
sco e being permitted to nn Measured as before, the angle 
— to was found to be 
iS process was reel poe —— times; the neutral 
point was found to recede lower and lower down the bea a the 
angle between a line drawn from the eye to the neutral point and 
pe axis of the beam falling successively from 54° to 49°, “3° and 
The distances, ce = measured, of the neutral point from the : 
ees corresponding t o the foregoing series of observations, were 
1st observation 2 feet 2 inches. 
9 (74 “ 6 “ 
nd 2 
8rd “cc 2 * 10 “ 
Ath “ 3 oe 2 ce 
“0 * So: : 3 
oe 4 <4 “c 
At the end of ehis series of experimen “es the ~sain of maxi- 
mum polarization had a become normal to the 
The laboratory was next filled with the fumes of gunpowder. 
In five successive experiments Se aaa ton to five different den- 
After the clouds of gunpowder ctl. cleared shin the laboratory 
was filled with the fumes of common resin, rendered so dense as 
2 Very irritating to my lungs. Thégdirection of maximum 
mere enclosed in this case an angle of 12°, or ee with 
axis of the beam. Looked at, as in the form , from 
a position near the electric lamp, 0 neutral pore was observed 
throughout the entire seiend t of the beam. 
Jour. Sci.—Srconp Serres, Vou. XLVI, No. 143.—Sepr., 1869. 
18 
