124 



Lightning Rods. 



Vol. V. 



loads per annum, of his neighbours ! If the 

 perusal of the above history will not move us 

 to be up and doing, in the way of collecting' 

 the moans of improvement contained in the 

 mines of wealth with which, in this country, 

 we are surrounded, and in some situations ab- 

 solutely choked with — witness our ponds and 

 ditches around many of our cattle-yards — I 

 know not what will ever be sufficient to move 

 us, until we are moved off the stage of life 

 by the rising generation, which seems to be 

 springing up for the purpose of correcting the 

 errors of their fathers, more particularly in 

 this respect than in any other; for it must be 

 admitted that there is too much truth in the 

 observation, " to the young it is that we are to 

 look for improvement." Stephen Gibson. 



For the Farmers' Cabinet. 

 Lightning Rods. 



Mr. Editor, — The interesting account un- 

 der this caption, at page 105 of the last num- 

 ber of the Cabinet, furnished by Mr. N. J. 

 Sharpless, is remarkable, and highly deserv- 

 ing the serious consideration and examina- 

 nation of your scientific readers. Here is a 

 conductor, perfect in all its parts, and erected 

 with the most scrupulous care and attention, 

 "going oft' at the proper angle from the 

 building, and embedded in charcoal, &c., 

 within the ground," and is nevertheless found 

 insufticient to ward oft" the effects of a highly 

 charged cloud, but down it the electric fluid 

 rushes; and while one portion thereof enters 

 the ground, another penetrates a two-foot 

 thick stone wall, separates again at the other 

 side, and traversing the building in a zio-zacr 

 direction, kills two cows which lie at a con*- 

 siderable distance, and at right angles one 

 from the other and the point at which the 

 fluid entered the building ! Now, it has been 

 said that an instance such as the above has 

 never occurred — that it cannot occur, if the 

 rod be perfect in all its parts — will your read- 

 ers favour us with their opinions on this very 

 important subject 1 



At page 379, of the 4th vol. of the Cabinet, 

 the question is asked, " whether the size of 

 the rod be of any importance to the safety 

 sought by the erection of a conductor? Much 



has been said as to its height and position is 



any consideration due to its diameter ?" In 

 answer, I beg leave to extract a few observa- 

 tions from a report on this subject, by Mons. 

 Gay Lussac, which tend, I think, to show that 

 in his estimation much of its safety depends 

 on the diameter of the rod — a circumstance 

 which has been generally overlooked. 



"The electric matter penetrates bodies 

 and traverses their substance, but with very 

 unequal velocities ; through some, which are 

 therefore called conductors, it passes with 



great rapidity ; such are, well-burnt charcoal 

 and water, vegetables, animals and the earth, 

 in consequence of the moisture they are im- 

 pregnated with and saline solutions ; but 

 above all, metals afford the readiest passage 

 to the electric fluid; and a cylinder of iroa 

 is therefore a better conductor than an equal 

 cylinder of water saturated with sea-salt, in 

 the ratio, at least, of a hundred thousand to 

 one ; and the latter conducts a thousand times 

 better than pure water. Non-conductors of 

 insulated bodies oppose great resistance to 

 the passage of electricity, through their sub- 

 stance ; such are, glass, sulphur, the earth, 

 stones and bricks, when dry, &c. No bodies, 

 however, are such perfect conductors as not 

 to oppose so?ne resistance to the electric fluid, 

 which, being repeated in every portion of the 

 conductor, increases with its length, and may 

 exceed that which would be offered by a 

 worse but shorter conductor. Conductors of 

 small diameter also conduct worse than those 

 of larger. The electric particles are mu- 

 tually repulsive, and consequently tend to 

 separate and disperse themselves through 

 space ; they have no affinity for bodies, and 

 reside oiily upon their surfaces, where they 

 are retained solely by the pressure of the at- 

 mosphere. The electric matter tends always 

 to spread itself over conductors, and to as- 

 sume a state of equilibrium in them, and be- 

 come divided amongst them in proportion to 

 their form, and principally to their extent of 

 surface. 



A lightning rod is a conductor which the 

 electric matter prefers to the surrounding 

 bodies, in order to reach the ground and e.x- 

 pand itself through it; but when it has any 

 breaks in it, or is not in perfect communica- 

 tion with the moist soil, the lightning, having 

 struck it, flies from it to some neighbouring 

 body, or divides itself between the two, in 

 order to pass more rapidly into the earth : 

 frequent instances of ruinous accidents have 

 occurred from both these causes." 



The last observation does not apply to the 

 rod mentioned by your correspondent, for that 

 was perfect in all its parts ; neither did the 

 electric fluid seem desirous of " passing more 

 rapidly into the earth," for, after it had 

 reached it, it turned and penetrated the wall 

 of the building, close to the surface of the 

 ground, through a thickness of two feet, and 

 was, after that, compelled to turn the angles 

 of two corners — where it left traces of its 

 passage — before it could reach the cows in 

 the yards. May we conclude, then, that the 

 diameter of the rod was not, in this case, suf- 

 ficient to conduct the whole of the electric 

 matter into the earth, and that a part, there- 

 fore, " flew from it," the bodies of the cov/s 

 acting as the next best conductors to the de- 

 structive fluid 1 C. J. 



