105 
showing that the electric force attracts all light bodies while the 
magnetic force attracts iron only. If, now, to these observations 
of Gilbert we add those of Von Guericke, in 1672,* that electrical 
repulsion exists as well as attraction ; of Boyle, the same year,} that 
the attraction between the electrified body and the light body is 
mutual; and that of Newton, in 1675,f, that the electric action 
will pass through glass, we have before us an epitome of electric 
science at the close of the seventeenth century. 
But the era of activity had begun. The light and sound of the 
electric spark were observed as early as 1708, by Wall,§ and their 
resemblance to lightning suggested. Hawksbee noticed, in 1709,|| 
the light which is produced when mercury is shaken in a glass tube, 
and had improved on the electrical machine of Von Guericke by 
using a globe of glass in place of one of sulphur. Gray, in 1729,9/ 
discovered the property of conduction, and divided bodies into 
electrics per se and non-electrics or conductors. Dufay discovered, 
in 1733, ‘‘that there are two kinds of electricity, very different 
from one another; one of which I call vitreous, the other vesznous, 
electricity. The characteristic of these two electricities is that 
they repel themselves and attract each other.’’ ** 
This, then, constituted substantially the whole of the electrical 
- knowledge of the world when the American Philosophical Society 
was established. Franklin, himself, took up the subject a few years 
later. He tells us that, ‘‘in 1746, being at Boston, I met there 
with a Dr. Spence, who was lately arrived from Scotland, and 
showed me some electrical experiments. They were imperfectly 
performed, as he was not very expert; but, being on a subject quite 
new to me, they equally surprised and pleased me. Soon after my 
return to Philadelphia, our library company received from Mr. Peter 
Collinson, F.R.S., of London, a present of a glass tube, with some 
account of the use of it in making such experiments. I eagerly 
seized the opportunity of repeating what I had seen at Boston, 
and, by much practice, acquired great readiness in performing 
* Experimenta Magdeburgica, Amsterdam, 1672, lib. iv, ¢. 15. 
+ Boyle’s Works, Vol. iv, p. 352 (edition of 1772, published in London in six volumes). 
{ Philosophical Transactions, 1675. Wiedemann, ‘‘ Lehre von der Electricifdt,” Vol. i, 
p. 4, 1882. 
2 Phil. Trans., v, 409, 1708. 
|| Physico-mechanical Experiments, 1709. 
{ Phil. Trans., vii, 449, 1727. 
** Mémoires de V Academie des Sciences, 1738, p. 457. 
PROC. AMER. PHILOS, SOC. XXXII. 143. N. PRINTED DEC. 14, 1893. 
