Morning journal and courier., 1891-09-01

the conductors at the corner of build
 ing, so that all parts will be equally pro- | tected.
 Though rods may be used, rain spouts
 will answer the purpose equally we'll.
 The physical laboratory of the Johns Hop kins university is protected from lightning by the roof and spouting. You can safe ly class all patented lightning rods as be-
 ing of little value beyond conducting rods
 that any man can put up himself, because the simple principle underlying all is that the lightning will follow the best conduc- tor. The idea 80 largely adopted in the erection of lightning rods, that small
 band of glass will prevent the electric current from passing to better adjacent conductor, seems playful. While it is true that lightning is attracted to an ele vated point or angle, when you cast your eyes over city like Baltimore and see the large number of such points and angles, the use of pointed rods fades into insig- nifcance as compared with the method of roofing with good conductor. This was illustrated by the incident of lightning striking the great monument in Washing ton several years ago. The monument is capped with a piece of aluminium, which has metallic connection with the ground by means of the iron work of the interior, but the lightning did not strike the top of the cap. It descended to some copper mixed in the side of the pyramidal, some distance from the apex burst portion of the stone, and, running along the copper into the interior, leaped without any me tallic connection to the iron framework, and passed to the ground. A framework of copper rods covering the angles, and csossing the sides of the immense cap, was recommended by me at that time for the future protection of the monument, and has probably been constructed The ground connection was to be through the internal ironwork spoken of. Somewhat similar to these methods is that of the Peabody library. The iron shelving con- nected with the metallic roof, and resting on stone foundation which might be shattered by stroke of lightning, has been connected with the ground by metal conductors, and no danger from lightning is apprehended.
 Lightning has no fixed portion of a building to strike. The stroke may fall at the center of the roof; and while it runs along the surface of body, the body may be broken or crushed by the enor nous pressure brought to bear upon it, in the same manner that an explosion of dy- namite or nitro-glycerine would cause a fracture. I have some fragments of church spire struck by lightning, which are bound together in their former rela- tive positions, but exhibiting all the frac lures produced by the concussion. There is a vast difference between the quantity of electricity and what is known as cleo trical pressure. This is illustrated in simple manner by the compression of the air. A small quantity of air can be com pressed to the same degree to obtain as great an expansive force as large qusnti- ty. The quantity of electricity in stroke of lightning is not nearly as much as pass es along almost any electric wire on the street, but the voltage or electric pressure of the street wire is rarely three thousand. A volt is the basis on which the pressure is estimated. The voltage of the light ming stroke is roughly estimated at six billion volts. In addition to this appalling difference, it may be said that the current of the wire is constant and continuing, while the lightning dart is delivered in the one two-hucdredth part of a second. Such an astounding force is capable of do- ing many strange things.
 In speaking of places of safety during an electrical storm, Dr. Rowland said that probably as safe place as any other would be an iron bedstesd, provided the ground connection is perfect, this being in line with the above theory, that the light ming would follow the best conductor.