The Doctrine of two different Electricities produc’d by exciting different Substances and of their Effects on each other seems to have been dropt after Monsr. Dufay—and those Effects ascrib’d to other Causes; which is an Instance that Science sometimes goes backwards. Many Years after, Mr. Kinnersley, a Friend of Dr. Franklin’s, being at Boston in New England, made some Experiments which again show’d that Difference of Electricities. He communicated those Experiments to Dr. Franklin, who repeated and explain’d them. See Franklin’s Letters.