Prince Rupert’s drops

Abstract

On 4 March 1660—61 ‘glass bubbles’ were first introduced to a meeting of the Royal Society. According to the minutes, ‘The King sent by Sir Paul Neile five little glass bubbles, two with liquor in them, and the other three solid, in order to have the judgement of the society concerning them’ (1). The Royal Society responded with remarkable celerity: its amanuensis produced some more drops two days later, which ‘succeeded in the same manner with those sent by the king’ (2). A very full report of the experiments performed was given to the Royal Society on 14 August 1661 by the President, Sir Robert Moray (3). As the Royal Society did not at this time have a normal publication series the report was recorded in the Register Book (4) and first published by Merret as an appendix to his translation of Neri’s Art of Glass (5). Henry Oldenburg lent Sir Robert’s account to the French traveller Monconys in 1663 who made his own translation into French of the prescription for making the drops. Monconys published this prescription in the second part of his Voyages (6). The ‘bubbles’— the solid ones, at least— were what were later to be called ‘Prince Rupert’s drops’. (Those said to contain ‘liquor’ could have been something different, but were probably the same containing vacuoles and no actual liquid.) These objects, glass beads with the form of a tear-drop tapering to a fine tail, made (though that was not generally known at the time) by dripping molten glass into cold water, exhibited a paradoxical combination of strength and fragility not without interest to the materials scientist of the present day, and which could not fail to excite the imagination of natural (and not so natural) philosphers of the 17th century. The head withstands hammering on an anvil, or, as a more modern test, squeezing in a vice, indenting its steel jaws, without fracture: yet breaking the tail with finger pressure caused the whole to explode into powder.