POPULA.lv SCIENCE REVIEW. 
580 
a preventive ; and arrived at the conclusion that the practice alluded to 
contained the elements of a very valuable means of preservation. M. Lappa- 
rent believes that the effect may be produced without any material destruc- 
tion of the wood, and that all that is required is a very thin coating or 
deposit of empyreumatic products, or, in other words, that the necessary 
carbonization may be obtained without any alteration of the surface of the 
wood, or any diminution of the sharpness of the angles, lie makes 
use of a jet of gas, mingled with a current of compressed air, in order at 
once to produce a more active combustion, and to give a more decided 
direction to the flame. It matters not what gas is used so that it give 
a great heat in burning. When the pieces of wood to be carbonized 
are small or light, they are passed over the flame of gas by hand, but 
in dealing with heavy timber, or with pieces fixed in position — such, for 
instance, as those of a ship upon the stocks — the heat is applied by 
means of a nozzle in connection with two elastic tubes, one supplying gas 
and the other atmospheric air under pressure. M. Lapparent says that 
specimens of wood of various kinds thus prepared have been placed in a 
dunghill side by side with unprepared pieces of the same timber, and that 
at the end of six months decay had attacked the latter in a decided 
manner, while the former remained perfectly untouched. 
This process is particularly recommended in the case of hard woods, 
which can with difficulty be impregnated with those antiseptic substances 
which are so effective with timber of the softer kinds. Wood prepared by 
M. Lapparent’s process is being submitted to trial in the Imperial dock- 
yards of France, and also by the railway companies ; and it is contem- 
plated to apply it also to carpentry and cabinet-making. We are also 
informed that similar trials are being made in the English dockyards. 
Imperfection of Lightning Conductors.— The attention of the 
French Academy of Sciences has been drawn by M. Perrot to the 
important question of the inefficiency of the conductors in general use. 
Three propositions, derived from a number of experiments, are laid down 
by M. Perrot : — 1st, that the surface of the conductor in contact with the 
water of the soil is generally so insufficient for the rapid dissemination of 
the electric current, that the conductor cannot be struck with lightning 
without becoming itself dangerous to the objects in communication with 
it ; 2udly, that the ordinary conductor is, however, sufficient to give pas- 
sage to a constant current of electricity sufficient to neutralize that of an 
approaching storm ; and, 3rdly, that in order to arm the common conductor 
against danger from thunderstorms, the rods should be furnished with a 
number of long, thin, divergent points of a high-conducting material. 
The experiments of MM. Pouillet and E. Becquerel have shown that pure 
ivater conducts electricity 0,754 millions of times less than copper, and 
M. Perrot therefore concludes that the surface of water in contact with the 
conductor should be that number of times at least more extensive than that 
of the copper. If, therefore, he says, the section of the conductor be equal to 
one square centimetre, the surface in contact with the water should be equal 
to 075,400 square metres, whereas it rarely amounts to more than the 
tenth of a square metre. The submerged surface of the conductor is there- 
fore generally about ten thousand times less than it should be, and presents 
