SCIENTIFIC SUMMARY. 
327 
is considerably diminished — in the instance he gives from 5° to l c . With 
his apparatus he has followed from zero to boiling point the rotation of the 
same current in sulphide of carbon and bichloride of tin. The molecular 
rotatory power is maintained as long as the boiling point is not approached. 
At that moment there is a diminution much more rapid than could have 
been foreseen from calculations based on the ratios of density. 
A Mirror Barometer. — M. Leon Tesserenc de Bort has ingeniously modi- 
fied the common aneroid barometer by substituting for the train of clock- 
work terminating in a pointer a mirror mounted on a jewelled axis, which 
is rotated by the rise and fall of the exhausted receiver, and its indications 
read off by a small telescope by reflection from a graduated scale. The 
sensibility of the instrument is said to be much increased, and all errors due 
to a long train of wheelwork are eliminated. 
Influence of Electricity on Colliding Water Drops . — Lord Rayleigh com- 
municates a paper to the Royal Society on this subject. It has been long 
known that electricity has great influence on fine jets of water ascending in 
a nearly vertical direction. In its normal state a jet resolves itself into 
drops, which even before passing the summit of the column, and still more 
after passing it, are scattered to a considerable width. When a feebly elec- 
trified body is brought into the neighbourhood of the jet, it undergoes a 
remarkable transformation, and appears to become coherent ; under more 
powerful electrical action the scattering becomes more marked than at first. 
The latter action is due to mutual repulsion of the drops ; the former has 
been hitherto unexplained. The cohesion seems to be more apparent than 
real ; the seat of sensitiveness is at the place of resolution into drops : each 
drop carries away with it an electric charge, which can be collected in an 
insulated receiver. He is able to show that the normal scattering is due to 
the rebound of the colliding drops ; such collisions being inevitable in con- 
sequence of the different velocities acquired by the drops under the action 
of capillary force, as they break away irregularly from the continuous 
portion of the jet. When the resolution is regularized by the action of 
external vibrations, as in Savart’s and Plateau’s experiments, the drops must 
still come into contact as they reach the summit of their parabolic path. 
Under moderate electrical influence, instead of rebounding after collision, 
they coalesce, and the jet is not scattered. This behaviour of the drops 
becomes apparent under instantaneous illumination, such as that of an 
induction coil, into the secondary circuit of which a Leyden jar is intro- 
duced. To obtain further evidence two similar jets were made to collide 
horizontally, one being in communication with the earth, the other supplied 
from an insulated cistern. The sensitiveness to electricity was extraor- 
dinary. A piece of rubbed gutta-percha brought near the insulated bottle 
at once determined coalescence. It was also possible to cause the jets 
again to rebound from one another, and then to coalesce. 
Besides statical electricity, the electro-motive force of a single Grove cell 
was sufficient to produce the same phenomena, one pole being connected with 
the water, the other to earth. Even the discharge of a condenser charged 
by a single Grove cell answered the purpose. The writer indicates in con- 
clusion the probable application to meteorology of the facts mentioned. 
The formation of rain must obviously depend materially on the consequences 
