Notes. 559 



be made to behave as a self-luminous source of light, by focusing 

 the light of the lamp-flame or other luminary upon the stop. This 

 will be found in no degree to impair definition, whether the hole in 

 the stop be large or small. 



The Optical Convention. 



At the Optical Convention which was held at the Northampton 

 Institute, Clerkenwell, from May 30 to June 3, with the object of 

 promoting the science and industry of Optics in Great Britain, the 

 President, Dr. K. T. Glazebrook, F.R.S., in his inaugural address, 

 passed in review the history of optical progress since early times, 

 dealing more particularly with a few periods of marked progress, 

 to show how theory and practice had acted and reacted upon one 

 another, and how necessary it was that close co-operation between 

 those interested in the scientific and technical sides of the question 

 should exist for the proper and prosperous development of British 

 Optical Industry. The first period selected for illustration was 

 the end of the seventeenth century, when the influence of the 

 work of Christian Huyghens and Sir Isaac Newton made itself 

 powerfully felt. Another period dealt with was about 100 years 

 later, when the researches of Thomas Young and Fresnel entirely 

 changed the whole of the theory on which the construction of 

 optical instruments depended. An example was also given of the 

 adverse and retarding effect of the want of co-operation between 

 science and practice. Early in the nineteenth century Sir George 

 Airy and Sir William Hamilton had investigated the aberration of 

 lenses. When a generation later Daguerre announced his inven- 

 tion, this work would have been of the greatest value to the 

 designers of photographic lenses. It was, however, forgotten, and 

 the last place where the practical opticians of that time might 

 have been expected to look for help were such publications as the 

 Transactions of the Cambridge Philosophical Society, or the Royal 

 Society of Dublin. They worked on empirical lines, with the 

 result that the main improvements had taken place in another 

 country, where the opticians had been quicker to recognise that a 

 full knowledge of the action on a lens of the light winch traverses 

 it was the condition precedent to further advance. 



The last illustration chosen to emphasise the beneficial effects 

 of intimate co-operation between science and industry was the 

 history of optical glass manufacture. After a brief reference to 

 the invention of optical glass by the poor carpenter Gunand in 

 1740, whose son, after his father's death, sold the secret to George 

 Boutemps, who was brought to England by Messrs. Chance, the 



2 p 2 



