SCIENTIFIC SUMMARY. 
441 
to either or to both. A third neutralizing plate is sometimes required in 
delicate observations. Lastly is an analyzing Nicol’s prism. 
The polarizer is first placed at 45° to the axis of the electric field, and the 
analyzer turned to complete extinction of the ray. The cell, with conduct- 
ing wires, is now interposed, and the light restored by the use of a hand- 
compensator, forming a fine streak passing midway between the balls in the 
cell. The cell is then charged with clean liquid, and the electrical machine 
is set at work. If carbon disulphide, by far the best dielectric yet discovered, 
be employed, a slight movement of the machine restores the extinguished 
light in the polariscope. As potential rises, the light becomes quite brilliant ; 
but on taking a spark from the prime-conductor, it vanishes instantly. There 
is no rotation of the plane of polarization, since slight contrary rotations of 
the analyzer affect the ray equally and similarly. Carbon disulphide appears 
to insulate completely, sparks drawn with the cell in circuit being of the 
same length as when it is removed. The action of dielectrified carbon 
bisulphide is therefore the same as that of glass extended in a direction 
parallel to the lines of force, and is a uniaxial birefringent action. Of the two 
component vibrations polarized in planes parallel and perpendicular to the 
lines of force, the latter is retarded. Weights are now attached to the com- 
pensating slips, causing strong permanent restoration from extinction of the 
light in the polariscope. If the machine be then worked, a broad horizontal 
band of darkness crosses the flame in the axis of the field, becoming by 
degrees perfectly black. With increased potential the flame reappears as a 
speck in the centre of the band, until the band is broken up into two on 
opposite sides of the axis, concave to one another. With rising potential* 
they move symmetrically outwards from the axis, dividing the flame into 
three large segments of equal brightness. When the electric action is near 
spark-discharge through the liquid, the bands cross the flame just outside 
the cylinder enveloping the two balls. This experiment represents the 
crossing of positive uniaxial plates. With a tension of 12 to 16 lbs., the 
bands are distinct, narrow, sharply defined, and very black. 
Benzol, toluol, xylol, cumol, cymol, terebene, and amylene, were tried in 
the same manner, yielding similar results. Carbon dichloride stands some- 
what above benzol. Nitrobenzol, tested in the usual way, acts as a good 
conductor, and gives no optical effect. If, however, the earth wire be dis- 
connected, and a spark taken from it to the band at the instant of discharge* 
there is a strong restoration of light from extinction. The same effect occurs 
less distinctly with amylene. 
Stannic chloride gave remarkable but not easily defined results. Young’s 
paraffin oil gave fine effects, similar to carbon disulphide. 
The fixed oils of olives, sweet almonds, poppy seed, rape seed, colza, 
mustard, linseed, nut oil, lard oil, and neatsfoot oil, acted oppositely to 
carbon disulphide. Animal oil, such as sperm, acted similarly to that sub- 
stance, and in an opposite manner to every other fixed oil. 
On the Capillary Phenomena of Jets is the title of a communication 
from Lord Rayleigh to the Royal Society. It is in a manner supplementary to 
a previous paper “ On the Influence of Electricity on Colliding Water Drops,” 
abstracted in our Summary of July. Water issuing from a circular orifice 
under pressure, though forming a contracted vein, remains circular. If the 
