The same letter recounts some of the tricks that Franklin and his fellow-experimenters were in the habit of making their new plaything perform. They fired spirits, lit candles just blown out, mimicked lightning, produced sparks with the touch of the finger, on the human hand or face, and gave electrical kisses. Other feats consisted in animating an artificial spider in such a way as to keep him oscillating in a very lifelike and entertaining manner between two wires, and lighting up the gilding on the covers of a book with a brilliant flash. This letter also shows that the provincial philosophers had already made improvements in the usual electrical methods. They had found that it was better to fill the phial with granulated lead than with water because of the superior facility with which the former could be warmed, and kept warm and dry in a damp place. They rubbed their tubes with buckskin, and, by observing certain precautions, such as never sullying the tubes by handling them, and keeping them in tight, close-fitting cases of pasteboard, lined with flannel, increased their efficiency. Their spheres for charging phials with electricity were mounted on iron axes with a small handle on one end, with which they could be set revolving like a common grindstone. It was in this same letter that Franklin with his usual generosity was careful to state that the power of pointed bodies to throw off as well as draw off the electrical fire was a discovery of his friend Hopkinson, and that the revolving sphere used by them was the invention of his friend Syng. About a month later, Franklin wrote to Collinson that, in the course of further experiments, he had observed several phenomena which made him distrust some of his former conclusions. "If there is no other use discover'd of Electricity," he said, "this however is something considerable, that it may _help to make a vain man humble_." Another letter from Franklin to Collinson, written about two weeks later, communicated to him some valuable observations upon "M. Muschenbroeck's wonderful bottle"--the Leyden Jar. This bottle was a mere ordinary bottle, with a common cork in its neck, into which a common wire had been inserted. He wrote that, at the same time that the wire and the top of the bottle were electrised positively or plus, the bottom of the bottle was electrised negatively or minus, in exact proportion; the consequence was that, whatever quantity of electrical fire was thrown in at the top, an equal quantity went out at the bottom until, if the process was kept up long enough, the point was reached in the operation, when no more could be thrown into the upper part of the bottle, because no more could be drawn out of the lower part. If the attempt was made to throw more in, the fire was spewed back through the wire, or flew out in loud cracks through the sides of the bottle.