To celebrate the bicentenary of the birth of Sir William Herschel, the first president of the Royal Astronomical Society, a conversazione was held in the rooms of the Society on November 15. Sir Arthur Eddington delivered the lecture with the above title twice during the evening (Occasional Notes, Boy. Astro. Soc., No. 3, January 1939). He pointed out at the beginning that in about thirty years the dimensions of the galactic system have been enlarged tenfold and the number of stars is now estimated to be 100,000 millions. It is remarkable that the picture of the universe which has resulted from modern research is very like the universe described by Sir William Herschel. His greatest enterprise was the systematic survey of the heavens, in the course of which he catalogued 2,500 nebulae and 800 double stars, and in all his research there was a definite plan to find out something about the structure of the universe. It seems remarkable that most of his observational work on the general distribution of stars and nebute was done with a reflector of only 19 inches aperture; the famous telescope of 4 ft. aperture was not a success and was not used very much. It is surprising that Herschel's speculations did not lead him astray more often. As one example, he assumed all stars to be of the same brightness, so that first magnitude stars were nearer than second magnitude stars, and so on. Actually, as we know to-day, apparent magnitude is a poor guide to distance. At the end of the lecture, Sir Arthur said that it is impossible for us to communicate with nebulas and receive a reply if they are more than 950 million light-years from us, owing to the speed of recession of the nebulae. It is expected that the 200-in. telescope will reach nebulae 1,000 million light years from us, so it is possible that we shall see galaxies with which it is impossible to communicate and receive a reply.