[573] It is not always necessary that the water should be cold; these
drops will be formed also in warm water, as well as in every other
fluid, and even in melted wax. See Redi’s experiments in Miscellan.
Naturæ Curios. anni secundi, 1671, p. 426. They succeed best with
green glass, yet I have in my possession some of white glass, which in
friability are not inferior to those of green.
[574] The navel, in German _nabel_, is that piece of glass which
remains adhering to the pipe when any article has been blown, and which
the workman must rub off. These navels, however, are seldom in so fluid
a state as to form drops.
[575] Journal des Voyages de M. Monconys, Lyon, 1666, 4to, ii. p. 162.
[576] Commentarius de rebus ad eum pertinentibus, Lips. 1719.
[577] Historia Naturalis. Edit. secunda, Londini 1680, 4to, p. 37.
[578] In his Observations on Neri Ars Vitraria, Amstel. 1668, 12mo.
[579] This is said, for example, by Grainger in his Biographical
History of England. London, 1769, vol. ii. part 2, p. 407.
[580] This book was only once printed, but the title-page has the date
1667. See Biographia Britannica, iv. p. 2654.
[581] Doppelmayer, p. 276.