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POPULAR SCIENCE REVIEW. 
nesium sulphate, rendered neutral by the addition of magnesium carbonate. 
One of these Tessels Was surrounded by a tube of sheet iron, in which was 
coiled a helix of insulated copper wire. A reducing current from one Smee 
cell was now passed through the solution in the two vessels, while another 
current from four Bunsen cells went through the magnetizing helix. At the 
end of twenty-eight days the wax rods were examined, with the following 
results : An equal weight of iron was deposited on each rod ; but, while the 
iron on the rod not exposed to the heliacal current was smooth and fair, the 
iron on the other rod was principally on its upper and lower portions, in 
the form of tufts, having a crystalline structure, and resembling somewhat 
the appearance presented by a bar magnet after its introduction into iron 
filings. He found that both deposits were very feebly magnetic, and further 
experiments showed that iron deposited by electrolysis receives a remarkably 
high charge of temporary magnetism, and has very feeble coercive force ; he 
therefore recommends such iron for the construction of electro-magnetic cores. 
decent Estimate of the Velocity of Light. — M. Cornu has, we understand, 
repeated, with all the precautions suggested by the recent progress in 
physical science, the experiment of Fizeau to determine the velocity of 
light. His researches, which have extended over a period of three years, 
lead him to conclude that the toothed wheel used in this method is capable 
of giving more accurate results than the revolving mirror employed by 
Foucault. The principal station, containing the toothed wheel and the 
mechanism for rotating it, the means of illumination, the telescope, the 
velocity-register, &c., was at the Ecole Polytechnique. The other| station, 
in which the collimating telescope and the reflector were placed, was at 
Mont Valerien. The distance between them was carefully measured and 
found to be 10,310 metres, with a probable error of less than ten metres. 
The wheel was carried upon the arbor of the minute-hand of an improved 
clock-work. Three of these wheels were made use of, having respectively 
104, 116, and 140 teeth. To the clock-work an electiic apparatus to 
register the velocity of rotation was attached, and also the means for regu- 
lating its motion, and even reversing its direction. A velocity of 700 to 
800 revolutions per second could be thus obtained, which was uniform, and 
perfectly under control. The registering apparatus consisted of a chrono- 
graph, upon the revolving cylinder of which three electro-magnetic pens 
made their marks ; one of these marked seconds, the second marked the 
rotations of the toothed wheel, and the third, controlled by a key in the 
hands of the observer, marked the instants of eclipse. The calcium-light 
was generally employed as the source of illumination, though a simple 
-petroleum lamp was also occasionally used. Over a thousand separate 
observations were made and registered upon the chronograph j but only the 
best of these, six hundred and fifty in number, were reduced. These re- 
ductions gave the following values in kilometres, for the velocity of light 
as deduced from the various orders of the occultation : — 
1st order. 2nd order. 3rd order. 4th. order. 5th order. 6th order. 7th order. 
302,600 297,300 298,500 298,800 297,500 300,400 
(17) (236) (376) (480) (91) (27) 
The numbers in parenthesis express the relative value of the corresponding 
