SCIENCE 



NEW YORK, MARCH 6, 1891. 



LIGHTNING-ROD PROTECTION. 

 What is the Problem ? 



In seeking a means of protection from lightning-dis- 

 charges, we have in view two objects, — the one the prevention 

 of damage to buildings, and the other the prevention of 

 injury to life. In order to destroy a building in whole or in 

 part, it is necessai'y that work should be done; that is, as 

 physicists express it, energy is required. Just before the 

 lightning- discharge takes place, the energy capable of doing 

 the damage which we seek to prevent exists in the column 

 of air extending from the cloud to the earth in some form 

 that makes it capable of appearing as what we call electricity. 

 We will therefore call it electrical energy. What this 

 electrical energy is, it is not necessary for us to consider in 

 this place ; but that it exists there can be no doubt, as it 

 manifests itself in the destruction of buildings. The problem 

 that we have to deal with, therefore, is the conversion of this 

 energy into some other form, and the accomplishment of this 

 in such a way as. shall result in the least injury to property 

 and life. 



Why have the Old Rods Failed ? 



When lightning-rods were first produced, the science of 

 energetics was entirely undeveloped ; that is to say, in the 

 middle of the last century scientiSc men had not come to 

 recognize the fact that the different forms of energy — heat, 

 electricity, mechanical power, etc. — were convertible one 

 into the other, and that each could produce just so much of 

 each of the other forms, and no more. The doctrine of the 

 conservation and correlation of energy was first clearly 

 worked out in the early part of this century. There were, 

 however, some facts known in regard to electricity a hundred 

 and forty years ago; and among these were the attracting 

 power of points for an electric spark, and the conducting 

 power of metals. Lightning-rods were therefore introduced 

 with the idea that the electricity existing in the lightning- 

 discharge could be conveyed around the building which it 

 was proposed to protect, and that the building would thus be 

 saved. , 



The question as to dissipation of the energy involved was 

 entirely ignored, naturally ; and from that time to this, in 

 spite of the best endeavors of those interested, lightning-rods 

 constructed in accordance with Franklin's principle have not 

 furnished satisfactory protection. The reason for this is ap- 

 parent when it is considered that this electrical energy exist- 

 ing in the atmosphere before the discharge, or, more exactly, 

 in the column of dielectric from the cloud to the earth, 

 above referred to, reaches its maximum value on the surface 

 of the conductors that chance to be within the column of 

 dielectric; so that the greatest display of energy will be on 

 the surface of the very lightning-rods that were meant to 

 protect, and damage results, as so often proves to be the case. 



It will be understood, of course, that this display of energy 

 on the surface of the old lightning-rods is aided by their 

 being more or less insulated from the earth, but in any 



event the very existence of such a mass of metal as an old 

 lightning-rod can only tend to produce a disastrous dissipation 

 of electrical energy upon its surface, — -"to draw the light- 

 ning,'' as it is so commonly put. 



Is there a Better Means of Protection ? 



Having cleared our minds, therefore, of any idea of 

 conducting electricity, and keeping clearly in view the fact 

 that in providing protection against lightning we must fur- 

 nish some means by which the electrical energy may be 

 harmlessly dissipated, the question arises, " Can an improved 

 form be given to the rod, so that it shall aid in this dissipa- 

 tion ? " 



As the electrical energy involved manifests itself on the 

 surface of conductors, the improved rod should be metallic; 

 but, instead of making a large rod, suppose that we make it 

 comparatively small in size, so that the total amount of 

 metal running from the top of the house to some point a 

 little below the foundations shall not exceed one pound. 

 Suppose, again, that we introduce numerous insulating joints 

 in this rod. We shall then have a rod that experience shows 

 will be readily destroyed — will be readily dissipated — when 

 a discharge takes place; and it will be evident, that, so far as 

 the electrical energy is consumed in doing this, there will be 

 the less to do other damage. 



The only point that remains to be proved as to the utility of 

 such a rod is to show that the dissipation of such a conduc- 

 tor does not tend to injure other bodies in its immediate 

 vicinity. On this point I can only say that I have found no 

 case where such a conductor (for instance, a small wire or 

 gilding) has been dissipated, even if resting against a plas- 

 tered wall, where there has been any material damage done 

 to surrounding objects. 



Of course, it is readily understood that such an explosion 

 cannot take place in a confined space without the rupture of 

 the walls (the wire cannot be boarded over i ; but in every 

 case that I have found recorded this dissipation takes place 

 just as gunpowder burns when spread out on a hoard. The 

 objects against which the conductor rests may be stained, 

 but they are not shattered. 



I would therefore make clear this distinction between the 

 action of electrical energy when dissipated on the surface of 

 a large conductor and when dissipated on the surface of a 

 comparatively small or easily dissipated conductor. When 

 dissipated on the surface of a large conductor, — a conduc- 

 tor so strong as to resist the explosive effect, — damage re- 

 sults to objects around. When dissipated on the surface of 

 a small conductor, the conductor goes, but the other objects 

 around are saved. 



A Typical Case of the Action of a Small Conductor. 



Franklin, in a letter to Collinson read before the Royal 

 Society, Dec. 18, 1755, describing the partial destruction by 

 lightning of a church-tower at Newbury, Mass., wrote, 

 "Near the bell was fixed an iron hammer to strike the 

 hours; and from the tail of the hammer a wire went down 

 through a small gimlet-hole in the floor that the bell stood 

 upon, and through a second floor in like manner; then hori- 



