While all Aeria was rejoicing over the return of the exiles and their restoration to the rights of citizenship, there was one of the inhabitants of the Valley who took little or no part in the festivities. This was Vassilis Cosmo, a man of between forty-six and forty-seven, and elder brother of the George Cosmo who had been chief engineer of the _Narwhal_, and was now first officer of the _Avenger_. A striking distinction of personality and temperament had, ever since he had reached a thinking age, marked him as one apart from the rest of his fellow-countrymen. He had little or none of the gaiety of disposition and social cordiality that were the salient characteristics of the Aerians as a people. He was serious almost to taciturnity, solitary and studious, and wholly engrossed in a single pursuit--the study of astronomy in its bearing on the great problem of interplanetary communication. After twenty years of constant labour, assisted by all the knowledge and inventive progress which had placed the Aerians so far ahead of the rest of the world, he had at length solved this problem and realised the dream of ages six years before Olga Romanoff had dropped her defiance from the skies. As yet, however, his success had been confined to one planet, and this, as will have been learnt from the conversation between Alma and Isma on that memorable night on which Alan’s letter had been received from the island, was the planet Mars. After infinite toil and innumerable failures, he had at length succeeded in establishing an intelligible system of what may here be described as photo-telegraphy, in which the rays of light passing between the earth and Mars were made to perform the functions of the electric wires in modern telegraphy. His alphabet, so to speak, consisted of a hundred great electric suns disposed at equal intervals on the mountain peaks round the great oval of the Valley. These were in direct communication with the observatory of Aeria, which was situated at a height of sixteen thousand feet on Mount Austral, the highest of the two snow-capped peaks which stood at the southern end of the Valley. A single switch key enabled him, when sitting by the huge telescope which embodied all the highest optical science of Aeria, to light and extinguish these brilliant globes as he chose, and it was by lighting and extinguishing them at certain intervals that he was able to transmit his signals to the Martian astronomer, who was waiting to receive them, and to reply to them by similar means across the gulf of thirty-four million miles which separates the two planets at their nearest approach to each other.