's
Micrographia (1665) It has been suggested that methods for making the drops have been known to glassmakers since at least the times of the
Roman Empire. Verifiable accounts of the drops from
Mecklenburg in North Germany appear as early as 1625. The secret of how to make them remained in the Mecklenburg area for some time, although the drops were disseminated across Europe from there for sale as toys or curiosities. The Dutch scientist
Constantijn Huygens asked
Margaret Cavendish, Duchess of Newcastle to investigate the properties of the drops; her opinion after carrying out experiments was that a small amount of volatile liquid was trapped inside. Although
Prince Rupert did not discover the drops, he was responsible for bringing them to Britain in 1660. He gave them to
King Charles II, who in turn delivered them in 1661 to the
Royal Society (which had been created the previous year) for scientific study. Several early publications from the Royal Society give accounts of the drops and describe experiments performed. Among these publications was
Micrographia of 1665 by
Robert Hooke, who later would discover
Hooke's law. His publication correctly laid out most of what can be said about Prince Rupert's drops—without a fuller understanding than existed at the time of
elasticity (to which Hooke himself later contributed) or of the failure of brittle materials from the propagation of cracks. A fuller understanding of
crack propagation had to wait until the work of
A. A. Griffith in 1920. In 1994,
Srinivasan Chandrasekar, an engineering professor at
Purdue University, and Munawar Chaudhri, head of the materials group at the
University of Cambridge, used high-speed framing photography to observe the drop-shattering process and concluded that while the surface of the drops experiences highly compressive stresses, the inside experiences high tension forces, creating a state of unequal equilibrium which can easily be disturbed by breaking the tail. However, this left open the question of how the stresses are distributed throughout a Prince Rupert's drop. In a further study published in 2017, the team, in collaboration with Hillar Aben, a professor at
Tallinn University of Technology in Estonia, used a
transmission polariscope to measure the optical retardation of light from a red
LED as it traveled through the glass drop, and used the data to construct the stress distribution throughout the drop. This showed that the heads of the drops have a much higher surface compressive stress than previously thought—at up to —but that this surface compressive layer is also thin, only about 10% of the diameter of the head of a drop. This gives the surface a high fracture strength, which means it is necessary to create a crack that enters the interior tension zone to break the droplet. As cracks on the surface tend to grow parallel to the surface, they cannot enter the tension zone, but a disturbance in the tail allows cracks to enter the tension zone. A scholarly account of the early history of Prince Rupert's drops is given in the
Notes and Records of the Royal Society of London, where much of the early scientific study of the drops was performed. ==Scientific uses==