I have 2 posts showing the famous photo from the fifth Solvay Conference in 1927. This photograph is very dear to my heart. I am sure many other physicists feel the same way.
Ernest Solvay was a “Belgian industrial chemist who began working in the chemical industry at the age of 21. He devised several methods for purifying gases, but he is best known for the development of a commercially viable ammonia-soda process for producing sodium carbonate and his invention of the Solvay carbonating tower (in which an ammonia-salt solution could be mixed with carbon dioxide). In 1861, he took out his first patent for soda production, in 1863 set up his first factory, and by 1890 Solvay had established companies in several foreign countries. By 1900, 95% of a greatly increased world production of soda came from the Solvay process.
This success brought Solvay considerable wealth, which he used for various philanthropic purposes, including the founding of various international institutes of scientific research in physiology (1893), sociology (1902), physics (1912), and chemistry (1913). The Solvay conferences on physics were particularly noted for their role in the development of theories on quantum mechanics and atomic structure.” 
Hendrik A. Lorentz was the chairman of the first Solvay Conference held in Brussels in the autumn of 1911. The subject was Radiation and the Quanta.
The subject of the 1927 Fifth Solvay Conference (17 of the 29 attendees were or became Nobel Prize winners) was Electrons and Photons. Hendrik A. Lorentz was the chairman of this conference as well.