SCIENTIFIC SUMMARY. 
389 
in the same direction, with her head to the north, and may therefore be 
expected to be strongly polarized. Should Mr. Hopkins’s method prove suc- 
cessful, he will have made a most important step in this difficult branch of 
science. 
Vapour Densities . — A memoir has been presented to the French Academy 
in which the author, M. H. St. Claire Deville described an experiment giving 
ocular proof of the dissociation of the vapour of perchloride of phosphorus 
at a high temperature. The following is the mode in which the experiment 
was made : — The author heated in an oil bath two colourless glass tubes, one 
containing a mixture of equal volumes of chlorine and air, the other per- 
chloride of phosphorus. The ends of the tubes, projecting a short distance 
from the bath, were flattened, so that the colour of the contents might ‘be 
observed and compared, a very minute opening being made, so that the 
expanded gases might escape. According to all analogy, the vapour of per- 
chloride of phosphorus should be colourless, and if at a certain moment it 
became yellowish-green, the natural inference would be that it contained free 
chlorine ; and at the temperature at which the two tubes possessed a yellow 
colour of equal intensity, it might be inferred that the decomposition of the 
perchloride was complete. Qualitatively, this experiment succeeded admirably. 
The colour of the chlorine was seen to be developed as the temperature rose, 
and no doubt of the dissociation remained ; but the author is as yet unable 
to obtain exact numerical results of the extent. — Vide Comptes Bendus , May. 
An Electrical Paddle-engine has been devised by and constructed for an 
Italian nobleman, General the Count de Molin. It is adapted to a small 
boat, which is intended to ply on the large lake of the Bois de Boulogne, 
and has the following construction : — There are two upright hoops, about 
2 feet 6 inches in diameter, placed 3 inches apart, in the periphery of each 
of which are encased 16 electro-magnets, placed opposite each other. Between 
these there is another hoop or wheel, of soft iron, of the same diameter as 
the others, and so articulated as to receive, when alternately attracted by the 
magnets at each side in succession, a sort of rolling from side to side, or 
“waddling” motion. To this wheel is fixed an axis about 7 feet long, which 
forms the prime moving shaft of the machine. When the wheel between 
the magnets takes its rolling motion, it causes the ends of this axis to describe 
circles ; one end turns the crank of a fly-wheel, while the other end is adapted 
to a framework, on the same principle as the pentagraph, which enlarges the 
motion received from the central disc, and communicates it in the form of a 
stroke by a connecting rod to a crank on the paddle shaft. This end of the 
moving bar also sets to work the distributors for alternately establishing and 
cutting off the electric communication between the magnets and the battery. 
There will be in all 16 elements of Bunsen’s. The force of the machine 
while at work with four elements was found to be one-quarter man-power, 
so that with 16 cells the power will be about that of a man. The paddle- 
wheels are 2 feet 6 inches in diameter. 
