VOL. LXVIII.] PHILOSOPHICAL TRANSACTIONS. 34p 



cylinder, was such as to cause a general tendency of it towards the less substi- 

 tute ; but, on account of the resistance wiiich seemed to operate at the surface 

 of the brass ball, it was there stopped, and by degrees accumulated, till such 

 time as the accumulation was great enough to overcome that resistance. Now, 

 according to this manner of reasoning, the point did not draw the fluid out of 

 the great cylinder silently ; but when the accumulation had got to a sufficient 

 degree, a sudden explosion ensued, more or less violent, according to the cir- 

 cumstances which accompanied the experiment. 



14th Observation. — From the other experiment it appears, that the rounded 

 end had not so great an influence as the point on the charge in the cylinder; 

 because we were obliged to bring it 5 times nearer before any light could be per- 

 ceived at all ; and even then it was so faint and inconsiderable in its diameter, 

 compared with the other light produced by the influence of the point, that it 

 manifestly confirmed the truth of the last observation. I shall now proceed to 

 make some general deductions from what has been already related. 



It seems to be clear then, that in all experiments made with pointed and 

 rounded conductors, the rounded ones are by far the safer of the two, whether 

 the lightning proceed from one or more clouds; that those are still more safe, 

 which (instead of being, as Dr. Franklin recommends, 10 feet high) are very 

 little, if at all, above the highest part of the building itself; and that this safety 

 arises from the greater resistance exerted at the larger surface. The luminous 

 appearance at the end of the brass ball, occasioned by the point in the 34th 

 experiment, manifestly showed that there was an accumulation of the fluid 

 within that part of the ball, in consequence of some resistance: for when the 

 resistance at the surface of the brass ball was at last overcome by the influence 

 the point had on the charge, the explosion took place immediately; and that, 

 not only between the two substitutes, but also between the end of the less sub- 

 stitute and the point. A cloud, therefore, that happens to be charged, and 

 within the striking distance of another cloud which is not charged, and also 

 equally within the influence of a pointed conductor, must necessarily produce 

 similar effects with those mentioned in the 34th experiment. On the other 

 hand, clouds that are circumstanced like those above, and not within the 

 influence of a rounded conductor, will pass quietly over such a termination, and 

 without any explosion. 



On acceleration, and its effects. — From considering the extraorflinary eff'ects 

 which have sometimes been produced on gross matter by lightning, and the 

 distance there frequently is between thunder-clouds and the earth, when such 

 effects take place, 1 suspected that those effects might in some degree be owing 

 to an increase of the velocity of the fluid which produced them. To try whe- 

 ther this was really so, it seemed necessary to have an apparatus of a far greater 



