Decembeb 17, 1909] 



SCIENCE 



867 



was laid on the direct path to earth being 

 chosen and on the necessity of including 

 with it or connecting to it other good paths 

 such as gas pipes, bell wires and the like. 

 There is no need of any special provision 

 of points. A blunt end will do as well, for 

 after all there is practically no silent draw- 

 ing off of the charge from the cloud, for it 

 is not an insulated conductor. The pro- 

 vision of a lightning conductor on a build- 

 ing undoubtedly increases its chances of 

 being struck by lightning, but if properly 

 arranged it also ensures that the structure 

 shall suffer no harm therefrom. Viewed 

 from our present standpoint it is a curious 

 historical fact that in 1777, just after the 

 war of the American revolution broke out, 

 a miniature verbal war between the advo- 

 cates of blunis and points, respectively, as 

 applied to lightning conductors raged. In 

 England party politics led many to con- 

 demn points as revolutionary and stick to 

 blu72ts. The Royal Society by majority 

 vote decided for points, but those who so 

 voted were considered friends of the rebels 

 in America. George III. took the side of 

 blunts. Franklin, who from the first had 

 prescribed points, wrote from France: 

 "The King's changing his pointed con- 

 ductors for blunt ones is a matter of small 

 importance to me. For it is only since he 

 thought himself safe from the thunders of 

 Heaven that he dared to use his own thun- 

 der in destroying his own subjects. ' ' The 

 king is reputed to have tried to get Sir 

 John Pringle, then president of the Royal 

 Society to work for blunts, but received the 

 reply: "Sire, I can not reverse the laws 

 and operations of nature." As stated 

 above, it matters not at all which we may 

 use. I have, indeed, seen a number of 

 cases in which the sharp points of lightning 

 conductors had been melted into rounded 

 ends by lightning. 



In the foregoing we have been consider- 



ing the effects of such ordinary discharges 

 of electricity as the disruptive spark, or 

 zigzag fla.sh. Apparently if the testimony 

 is reliable there are other and more rare 

 forms of discharge. I allude to .sheet light- 

 ning, so-called globular lightning and to 

 bead lightning. But it may be asked, why 

 call sheet lightning a rare form? It is, 

 indeed, true that when a storm is so far 

 distant that the spark discharges can not 

 be seen, as when it is below the horizon, or 

 when the spark is blanketed by a mass of 

 mist or cloud there is to be noted a diffused 

 light or extended illumination, which, on 

 account of distance, may not appear to be 

 attended by thunder. This and similar 

 effects are often called sheet lightning. 

 From observations during a few heavy 

 storms, however, I am led to infer the exist- 

 ence at rare intervals of a noiseless dis- 

 charge between cloud and earth— a silent 

 effect attended by a diffused light, and 

 which may be the true sheet lightning. In 

 my experience it has accompanied an un- 

 usually heavy downpour of rain, the whole 

 atmosphere where the rain fell most heavily 

 being apparently momentarily lighted up 

 by a purple glow, seemingly close at hand 

 in the space between the rain drops. The 

 appearance has been seen in the daytime 

 as an intense bluish or purplish momentary 

 glow without any accompanying sound. It 

 could scarcely have been illu-sory. It is 

 hoped that other observers will carefully 

 note any such like effect if it occurs. It is 

 certainly a rare phenomenon. 



It is quite common that any very bright 

 flash, the details of which from its sudden- 

 ness and intensity are unobservable, be 

 alluded to as a ball of fire. Doubtless 

 many of the reported cases of so-called ball 

 or globular lightning may be explained as 

 instances of this condition of things. 

 Nevertheless, there are so many recorded 

 instances, apparently in substantial agree- 



