306 PETER GUTHRIE TAIT 



thinking of a mode of keeping out missiles, having no notion that a thin shell of 

 soft copper would have been quite as effective as massive iron. But those emperors 

 who, as Suetonius tells us, wore laurel crowns or sealskin robes, or descended into 

 underground caves or cellars on the appearance of a thunderstorm, were not protected 

 at all. Even in France, where special attention is paid to the protection of buildings 

 from lightning, dangerous accidents have occurred where all proper precautions seemed 

 to have been taken. But on more careful examination it was usually found that 

 some one essential element was wanting. The most common danger seems to lie 

 in fancying that a lightning-rod is necessarily properly connected with the earth if 

 it dips into a mass of water. Far from it. A well-constructed reservoir full of 

 water is not a good " earth " for a lightning-rod. The better the stone-work and 

 cement the less are they fitted for this special purpose, and great mischief has been 

 done by forgetting this. 



A few years ago the internal fittings of the lighthouse at Skerryvore were 

 considerably damaged by lightning, although an excellent lightning-rod extended 

 along the whole height of the tower. But a long copper stove-pipe, rising through 

 the whole interior of the tower, and the massive metallic ladder rising from the 

 ground to the lowest chamber, though with a considerable gap between them, offered 

 less resistance than the rod, for the lower end of the ladder was nearer to the sea 

 than was the pool on the reef into which the lightning-rod plunged. Hence the 

 main disruptive discharge took place from the stove-pipe to the ladder, blowing 

 the intervening door to pieces. The real difficulty in these situations, exposed to 

 tremendous waves, lies in effecting a permanent communication between the lightning- 

 rod and the sea. But when this is done the sea makes far the best of " earths." 



When a lightning-rod discharges its function imperfectly, either from insufficient 

 conducting power or because of some abnormally rapid production of electricity, a 

 luminous brush or glow is seen near its point. This is what the sailors call St Elmo's 

 Fire, or Castor and Pollux. In the records of mountain climbing there are many 

 instances of such discharges to the ends of the alpenstocks or other prominent 

 pointed objects. One very remarkable case was observed a few months ago in 

 Switzerland, where at dusk, during a thunderstorm, a whole forest was seen to 

 become luminous just before each flash of lightning, and to become dark again at 

 the instant of the discharge. 



Perhaps the most striking of such narratives is one which I will read to you 

 from the memoirs of the Physical and Literary Society, from which sprang the 

 Royal Society of Edinburgh. These Essays are rare and curious, and the names of 

 Maclaurin, James and Matthew Stewart, Whytt, and Monro, appear among their 

 authors. 



The following observations on Thunder and Electricity by Ebenezer McFait, M.D., 

 show how, in the search for truth, men may unwittingly put themselves in the gravest 

 danger: 



"The experiment proposed by Mr Franklin, to prove that lightning and the electrical 

 fire are the same, has often been repeated with success both in England and abroad, so that 

 the most noted electrical experiments have been performed by fire drawn from the clouds. 



"Mr Franklin also first discovered that sharp points attract and discharge the electrical 



