What this centre may be, whether a great sun like Sirius, one hundred times larger than ours, with unknown powers and unknown uses, is of course only conjecture.
Herschel gave much attention to nebulæ, discovering and describing twenty-five hundred new nebulæ and clusters. He gave his life to the study of the construction of the heavens. Concerning his statement of the general construction, Professor Holden, himself a brilliant astronomer, says: "It is the groundwork upon which we have still to build.... As a scientific conception it is perhaps the grandest that has ever entered into the human mind. As a study of the height to which the efforts of one man may go, it is almost without a parallel.... As a practical astronomer he remains without an equal. In profound philosophy he has few superiors. By a kindly chance he can be claimed as the citizen of no one country. In very truth his is one of the few names which belong to the whole world."
The distinguished man, though unassuming and gentle in manner, must have had a realizing sense of the greatness of his work, for he said, "I have looked further into space than ever human being did before me. I have observed stars of which the light takes _two millions_ of years to travel to this globe."
He gave much study to light and heat. So boundless was his knowledge believed to be, that a farmer called one day to ask the proper time for cutting his grass.
"Look at that field," said the scientist, "and when I tell you it is mine, I think you will not need another proof to convince you that I am no more weatherwise than yourself or the rest of my neighbors."
He worked earnestly till he was seventy-six, always depending upon his faithful and inseparable Caroline for aid in his labors. He made a telescope for her, with which she swept the heavens for comets, finding eight, five of which she discovered for the first time.
At seventy-six his health began to fail. He had worked incessantly from his struggling boyhood, but brain work does not wear us out; care and anxiety bring the marks of age upon us. He now took little journeys away from Slough for change of scene and air, while Caroline stayed at home to copy his papers for the Royal Society, and to arrange his manuscripts. In 1816, he was made a knight of the Royal Hanoverian Guelphic Order, by the Prince Regent, and in 1821 was the first president of the Royal Astronomical Society, his son being its first foreign secretary.