116 
POPULAR SCIENCE REYIEW. 
Luminous Visibility of the Electric S]oa7'k . — Mr. Felix Lucas concludes, from 
very original theoretic considerations, that the luminous distance at which 
the electric spark is visible is greater than that of a permanent light, the 
apparent intensity of which would equal 250,000 times that of the spark. 
The light actually employed to illuminate our new lighthouses gives a 
brilliancy equal to 125 carcel lamps. An electric spa]-k possessing the illu- 
minating power of the 200th part only of a carcel burner, is superior as to 
its power of projecting light. Hence we can conceive the immense effect of 
a warning light composed of intermittent flashes of the electric spark proceed- 
ing from a strong Leyden jar battery. Mr. Lucas states that, in an experi- 
ment made in a laboratory, two apparatuses were established, one voltaic 
equal to 125 carcel lamps, and another spark-battery equivalent to only the 
l-2000th part of a carcel wick. The photometer (such as is employed in 
the lighthouse administration) showed a marked superiority in favour of the 
spark. — Vide Chemical Neios, October 4. 
The Baromeb'oyraph is the term given by M. Breguet to an application of 
the automatic principle of registration to the barometer. It consists of four 
metallic boxes, the upper and lower of which are undulated (the usual 
aneroid barometer) j a vacuum is made in each of these boxes separatel}^, and 
they are attached to a chain the movement of which is four times greater 
than that of a single box for the same variation of pressure. A steel spring 
of great strength acts upon these boxes in a contrary direction to the 
atmospheric pressure, and communicates with an indicating lever. The 
registration is effected on a cylinder which revolves by means of an ordinary 
clock 5 it makes a complete revolution in a week and carries a glazed paper, 
which is covered with lamp-black by being held over the flame of a candle ; 
the extremity of this lever, very flne and pointed, traces a line of variations 
in a white streak. The periods (four times a day) are represented on the 
diagram by vertical lines, and the barometric readings by horizontal lines 
placed a millimetre apart, the arm of the indicator being so arranged as to 
mark the variations on the same scale as a common mercurial barometer. 
This instrument, says the Abbe Moigno, has none of the errors of the 
common aneroid barometer resulting from the great number of pieces, levers, 
articulations, gearing, connecting chains, and springs. 
Vai'iations in Electrolytic Towers.— one of the meetings of the French 
Academy, M. Edmund Becquerel described certain experiments of M. Bou- 
chotte on the electrolytic powers of the currents of the magneto-electric 
machine of the Atlantic Company. From the experiments it seems,|^that 
when the current sent by the commutator is always in the same direction, 
the electrolytic power is that of 144 Daniell elements with sulphate of cop- 
per ; but when the current is alternate, as in the production of the electric 
light, the electro-motive power is nil. — Vide Compte Renclus, Nov. 4. 
Eractical Value of the Eolariscope . — The practical application of the laws of 
polarisation of light in the case of the saccharometer is well known to our 
readers. The value of this instrument is, however, well demonstrated by an 
experiment recently carried out by M. Dubrunfant : — Two samples of 
AVest Indian sugar. No. 10, of the same shade of colour, and apparently of 
the same commercial value, after being submitted to the saccharometer, 
w'ere a‘'certained to contain 93'00 and 88-00 parts of saccharine matter re- 
