Page 20 - Spring 2009

ing a perfect experimental demonstration of this remarkable phenomenon in both its varieties.” Young (1807) and Fresnel (1819) (see Table 3) had previously performed experiments to explain this refraction phenomena but the experiments performed between 1831 and 1833 by Lloyd were character- ized by such experimental skill and clarity as to set them apart.
The conical refraction experiment definitively verified the predictions of Hamilton and was perhaps the earliest combina- tion theory and measurement to describe the wave nature of light. The results of the conical refraction experiment were con- sidered important as there was still considerable debate as to whether projectile, fluid, vibration or wave theory was the cor- rect theoretical description of optical interference effects Cantor (1983). He prepared a progress report on optical science for the British Association between 1833 and 1834. Shortly after, in 1834, he performed the mirror experiment shown in Fig. 7. And described his results to the Royal Irish Academy.
The importance of the elegant design and clarity of the result along with the wave theoretic explanation were imme- diately recognized. In fact, his analytical explanation is simi-
lar to that described here and found in Physics of Sound in the Sea. Lloyd recognized the importance of the phase of his reflection from his polished glass and concluded that a phase change of π resulted. He also recognized that the introduc- tion of a phase shift on the direct wave, the piece of mica, that would shift the pattern so that the complete interference pat- tern could be observed. His estimation of the peak intensities and observations of the nulls were clearly explained in his paper read in 1834 and published in the Transactions in 1837. Mach (1926) cites a later experiment by Billet (Table 3) that produced comparable results; but it was the experiment by Lloyd that was considered most seminal. These early con- tributions to optics were probably the reason he became a Fellow of the Royal Society in 1836. Selected optical refer- ences to Lloyd are appended for those interested in his texts and original works.
Between 1831 and 1833 the British Association decided to conduct surveys of the terrestrial magnetism field intensi- ty in the kingdom. A standing committee, including Lloyd was formed and he undertook to make the required observa- tions in Ireland with Captain Sabine. He developed, along
Table 4. Major contributions
A Treatise on Light and Vision (1831)
Conical Refraction through Bi-axial Crystals (1831-1833) Lloyd's Mirror Experiment (1834)
With Sabine measurement Instrument for magnetic fields (1834) Establishment: School of Eng. at Trinity College (1841)
Type 45BM
The KEMAR Manikin
is now available for telephone testing
Mount your telephone in any position with Handset Positioner Type 45EA
Mouth Simulator according to ITU-T Rec. P.58 with built-in power amplifier
Ear and pinna simulator according to ITU-T Rec. P.57 Type 3.3
US office 23621 Lorain Road · North Olmsted · OH 44070, USA · E-mail: sales@gras.us · www.gras.us
Lloyd’s Mirror 19