favour what is known as the Melsens system, due to Professor Melsens, of
Brussels, and Professor Zenger, of Prague, but first suggested by the late
Professor Clerk-Maxwell. In a paper read before the British Association,
Clerk-Maxwell proposed to protect powder-magazines from the effects of
lightning by completely surrounding or encasing them with sheet metal, or
a cage of metallic conductors. There were, however, several objections to
his system as he left it.

Professor Melsens[A] has, while using the idea, made several important
alterations. He has multiplied the terminals, the conductors, and the
earth-connections. His terminals are very numerous, and assume the form of
an aigrette or brush with five or seven points, the central point being a
little higher than the rest, which form with it an angle of 45°. He
employs for the most part galvanised-iron wire. He places all metallic
bodies, if they are of any considerable size, in communication with the
conducting system in such a manner as to form closed metallic circuits.
His system is illustrated in Fig. 2, taken from _Arms and Explosives_.

[Footnote A: Belgian Academy of Science.]

This system is a near approximation to J.C. Maxwell's cage. The system was
really designed for the protection of powder-magazines or store buildings
placed in very exposed situations. Zenger's system is identical with that
of Melsens, and has been extensively tried by the Austrian military
authorities, and Colonel Hess has reported upon the absolute safety of the
system.

[Illustration: Fig. 3.--FRENCH SYSTEM OF LIGHTNING CONDUCTORS.]

The French system of protecting powder-magazines is shown in Fig. 3, where