172 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



series of experiments as to the capacity of copper and iron to 

 transmit electric force. He states that Melsens demonstrates 

 that an electric discharge does not of necessity pursue the 

 shortest and easiest path. As to the density of copper and 

 iron when subjected to the disintegrating dispersion of elec- 

 trical discharges of high tension, he states that under the 

 same circumstances the cop])er wire used as a conductor for 

 a charge from fifteen very large Leyden jars is completely 

 dissipated into a trail of black dust, while the iron wire is 

 not even broken under the same circumstances, but is simply 

 beaded along its entire length by a series of successive pro- 

 tuberances. Professor Melsens has adapted a very elaborate 

 system of about 428 points belonging to as many iron rods 

 to the protection of the Hotel de Ville at Brussels from light- 

 ning. The rods are collected ultimately into a group of 

 eighteen larger stems, which are soldered into a continuous 

 metallic mass, from w^hich they ultimately diverge under- 

 ground to the w^ater-pipes, gas-pipes, and moist ground ; se- 

 curing a triple earth contact which would seem to present 

 perfect assurance against danger. Melsens entertains the 

 magnificent design of protecting the entire town of Brussels 

 in one continuous system of rods, so that by securing a very 

 ample development of earth contacts beneath, and air termi- 

 nals above, no possible danger can be apprehended for the 

 whole surface of the town. Quarterly Journal British Me- 

 teorological Society^ 1876, 48. 



LIGHTNING-CONDUCTORS. 



Dr. R. J. Mann states that the following conditions are in- 

 dispensable for protection against lightning : first, ample 

 dimension and unbroken continuity in the lightning-rod ; 

 second, free earth contacts, with frequent examination by 

 galvanometers of the condition of these to prove that there 

 is no gradual impairment through the operation of chemical 

 erosion ; third, the employment of points enough to dominate 

 all parts of the building ; fourth, the addition of terminal 

 points to the conducting system wherever any part of the 

 structure of the buildino^ comes near to the limitino; surface 

 of a conical space, having the main point of the conductor 

 for its height, and a breadth equal to twice the height of that 

 point from the earth for the diameter of its base ; fifth, the 



