attraction of an invisible satellite moving around the bright star. Some years afterwards Dr. C. A. F. Peters, by a careful study and comparison of all the observed right ascensions of Sirius, was able to calculate the orbit of the attracting body. Afterwards Mr. T. H. Safford was led to the same result by a study of all the observed declinations of the star, so that there could no longer remain any reasonable doubt that the satellite really existed, though it continued to elude the most careful search. On the evening of January 31, 1862, Alvan G. Clark, pointed the newly finished glass at Sirius, probably without any knowledge of the researches to which we have alluded. "Why, father," he exclaimed, "there is a companion!" The father looked. There was the satellite surely-distance about ten seconds. As the news went round the world, every great telescope was pointed at Sirius. Now, when it was known exactly where the companion was, it was found that many telescopes would show it, and measures of its distance and direction flowed in from all quarters. The French Academy of Sciences awarded Mr. Clark the Lalande medal, which is given annually to the maker of the most interesting discovery of the year. It was awarded not simply for the discovery, but also for making the object glass which led to it. The important question whether the satellite was really the disturbing body. which had been predicted, could only be settled by long continued observation. After four years it was found that the observed position and motion of the satellite both corresponded so nearly with those predicted from theory that no serious doubt of the identity of the seen and unseen bodies could be entertained. Mr. Clark commenced the construction of this telescope for the University of Mississippi; but the outbreak of the civil war necessarily prevented that institution from completing its contract, and the glass was sold to the Chicago Astronomical Society. It was placed in charge of Mr. T. H. Safford, the distinguished astronomer and computer of Cambridge. Very little has, however, been done with it, as the architectural defects of the dome in which it is mounted have interfered with its use. During all the time of which we have been speaking, while observatories supplied 66 with large telescopes were springing up all over the country, and while an association of private gentlemen had supplied themselves with the largest refracting telescope ever made, the great telescope of the National Observatory of the country was nothing more than a 91⁄2 glass, mounted with all the ancient inconveniences. This was clearly a state of things which called for improvement, but a remedy was by no means easy. When the war had to be prosecuted; when the national debt was to be paid off; and when Mr. E. B. Washburne, the watchdog of the treasury," presided over the House Committee on Appropriations, asking Congress to vote money for a telescope seemed, indeed, a hopeless enterprise. However, in the summer of 1867, the writer sought an interview with Mr. Clark, to learn on what conditions he could be induced to undertake a telescope for the Government of not less than two feet clear aperture. He was not at all enthusiastic on the subject. He was willing to undertake the work for forty thousand dollars in gold, but would not make a contract on any other than a gold basis, for fear of a subsequent depreciation of the currency. This condition was very embarrassing, as it was not at all likely that Congress could be induced to authorize a gold contract within the country, and the project seemed so hopeless that no further attempt to carry out the scheme was then made. In the course of the year following the necessity of some action, if the Observatory was ever to have the telescope, became apparent. Rumors that some one else would order the instrument came in from various quarters, and, especially, from Princeton College, where they had gone so far as to project a building for it. As it did not seem likely that Mr. Clark would be able to undertake more than one instrument of the size desired, and as this was expected to occupy more than four years in its completion, prompt action. seemed urgently necessary. Accordingly, in his annual report of 1868, Rear Admiral Sands set forth the wants of the Observatory, and the ability of Mr. Clark to supply it, and asked for four annual appropriations, each of ten thousand dollars in gold, to pay for the telescope. But the words were spoken to the empty air. Secretary Welles had adopted the rule that no estimates for improvements in any branch of the Naval service should be sent to Congress with his sanction, but that expenditures should be confined to what was necessary to keep the public property in repair, and carry on the necessary operations of the Navy on the most limited scale, unless Congress should see fit to authorize more on its own responsibility. The telescope being clearly an improvement, the estimate for its construction could not reach Congress through the proper official channel at all. If Congress had been aware of this rule adopted by the Secretary of the Navy, and had known that the nonappearance of an item of this kind in his estimate by no means indicated disapproval on his part, its ear might still have been obtained for the project. But the Committee on Appropriations did not know anything of the sort, and no amount of statement or explanation could make them aware of it. They looked to the Secretary of the Navy for all estimates for the Naval Observatory, and knew nothing about any except those he recommended. ought not to be," said one of the Senators. "Why is so great a deficiency not supplied?" Mr. Hilgard adduced the supposed reluctance of Congress to appropriate money for a telescope. "But it must be done. You have the case properly represented to Congress, and we will see that an appropriation is passed by the Senate, at least.' Mr. Hilgard did not lose a day in following this advice. He called upon the Superintendent of the Observatory, who of course gladly assented to the plan. He then communicated by telegraph with a number of the leading men of science throughout the country, who authorized their signatures to the proper petition. The latter called attention to the wants set forth by the Superintendent of the Observatory in his last two annual reports, and to the ability of the Messrs. Clark to supply this want. It was duly printed, and put in the hands of Senator Hamlin for presentation to the Senate within three or four days of the dinner party. The proposed measure being considered by the Committee on Naval Affairs, and on Appropriations, was adopted in the Senate as an amendment to the Naval Appropriation bill, without opposition. The great difficulty now was to get the amendment through the House of Representatives, or rather through its Committee on Appropriations, as the session and the bill were together in a stage where everything had to be decided by the appropriate committees. The recommendation was renewed the year following, but with no better immediate effect. If we were writing only the official history of the project, we should have but to say that about the close of the following session, in July, 1870, Congress suddenly changed its mind, and authorized the telescope. But to explain how Congress came to change its mind, we must intrude upon a private dinner party, given by one of our most honored citizens, trusting for pardon to the great public importance of a movement which originated over the table. Among the party were Senators Hamlin and Casserly, Mr. J. E. Hilgard, of the Coast Survey, and a young gentleman from New York who had spent the day in examining the sights of Washington. Being called upon for an account of what he had seen, he described his visit to the Observatory, and expressed his surprise at the absence of a large telescope, the largest there not only being much smaller than many at quite unknown observatories, but smaller than Mr. Rutherfurd's in New York. The Senators listened to this statement with incredulity, and appealed to Mr. Hilgard to know whether the visitor was not mistaken through a failure to find the largest telescope of the Observatory. The latter replied that the statement was entirely correct, the telescope having been procured at a time when the success of largely ones was still considered doubtful. "This To prevent misapprehension we must say that no government is more ready than our own to appropriate money for scientific objects of the value of which it is fully satisfied, when the case is properly presented and fully understood. The great difficulty (greater, perhaps, than would be supposed outside of Washington,) is to secure such presentation and understanding. It may be safely assumed that a member of Congress never looks at any printed document sent him through the mail, so that personal application is the only way of calling his attention to any subject. After a canvass of the House Appropriation Committee, it was believed that a clear majority was in favor of the measure; we were therefore much surprised to find that it recommended non-concurrence. This left the question to the joint committee of conference, which fortunate comprised such men as Drake, of the Senate, and Niblack, of the House. There the telescope was agreed to, and the clause authorizing its construction speedily became a law. The price was limited to fifty thousand dollars, and ten thousand were appropriated for the first payment. About the time the bill passed, an occurrence threatened to complicate matters exceedingly, and perhaps endanger the possession of the telescope by the Government. Mr. L. J. McCormick, of reapingmachine fame, had conceived the idea of getting the largest telescope that could be made for an observatory he intended to McCormick's withdrawal of his claim to it. Another circumstance which probably facilitated the undertaking was that a rival house had meanwhile arisen in England, in the persons of Thomas Cooke & Sons, of York, who had made a glass of twentyfive inches aperture for R. S. Newall, Esq., of Gateshead, England. This glass was much larger than that of the Chicago telescope; a state of things to which the Clarks were by no means disposed to submit. But for this, it is doubtful whether they could have been induced to under found, and sent an order to the firm of Alvan Clark & Sons while the appropriation was still pending in Congress. Mr. Clark, however, believed that he could complete a pair of twin instruments almost as quickly as a single one, and in one way the contract with Mr. McCormick facilitated that with the government. It being made on a gold basis, Mr. Clark was quite willing to enter into the government contract on a currency basis, which removed one of the principal difficulties in its way. The question who should have the first telescope was amicably settled by Mr. VOL. VII.-4 take anything larger than twenty-four inches, but they now very readily consented to try twenty-six. While negotiating the contract, the writer contended persistently for some provision which would enable the government to secure a larger telescope than Mr. McCormick, but they would agree to nothing of the sort, the supposed right of that gentleman to a telescope of equal size being guarded as completely as if he had been a party to the negotiations. As the only establishment in the world to be entrusted with the making of the in strument was that of the Clarks, so only a single firm could be relied on to furnish glass discs of the necessary size and purity for the lenses, namely, that of Chance & Co., of Birmingham, England, from whom Mr. Clark had procured nearly all his optical glass during the twenty years he had been making telescopes. As soon as the contract with the government was completed, George B. Clark, the same who melted the bell in the kitchen fire twenty-seven years before, crossed the ocean and proceeded to Birmingham to contract with Chance & Co. for the glass. Making discs of the required size proved to be a task of such difficulty, that more than a year elapsed before entire success was reached, a number of trials having failed in the meantime. 1871. By the terms of the contract the To give our readers a clear idea of the subsequent operations, we must describe the construction of an achromatic object glass, or objective, as it is usually termed. Every one knows that when light passes through a refracting surface it is decomposed, or separated into a number of prismatic colors. The result of this is that a lens cannot bring all the rays from a luminous object to the same focus, the focus for red rays being always more distant than that for blue rays, so that there is no distinct image. In consequence, Newton and his contemporaries considered the construction of refracting telescopes which would show an object with entire distinctness to be impossible. But Dollond, an English optician of the last century, conceived the idea of combining two lenses of different kinds of glass and of opposite curvatures, in such a way that each should counteract the effect of the other in decomposing the light, but should leave an outstanding difference in their refracting power, and thus bring all the rays to the same focus. The two sorts of glass-tion thus used are flint and crown glass, of which the former has about double the dispersive or decomposing power of the latter. An accompanying figure shows the section of an objective, as made by the Clarks. It will be seen that the flint glass has only one curved surface, while the crown has If This first test having been successful on both glasses, that by polarized light was applied. Hearers of Professor Tyndall's lectures last winter may remember how, by curiously enough, it disappeared during the grinding, so that when the lenses were completed, no trace of unequal annealing could be seen. The application of these tests was completed early in January, 1872, and the work of grinding was immediately commenced. Owing to the great size of the glasses the first rough grinding was done by machinery, the "grindstone" being a rapidly revolving iron wheel, over which a stream of water and sand was kept running. The glasses were thus roughly brought to the desired shape in a few days. The forms chosen were much more simple than those usually employed in SECTION OF OBJECTIVE. simply submitting a piece of glass to pressure, while polarized light was passing through it, he was able to change its action on the light in a remarkable manner. This property of polarized light affords the most delicate test of the equal annealing of glass. To apply the test, the glasses were taken into the open air, and laid on the ground upon a piece of black cloth. Each 'glass was then viewed in such a way that the light of the sky or clouds should. be reflected from THE NEW WASHINGTON TELESCOPE. its under surface, and reach the eye after twice traversing its thickness. This light was viewed through a Nicol's prism held in the hand, and turned round and round, the glass also being turned round so that the light should be examined in all directions. The result indicated that the flint glass was perfectly uniform, while in the crown there were very slight circles of strain from the center to the circumference. This defect would not interfere with the usefulness of the glass, and large glasses, the crown glass being double convex, with an equal curvature on each face; the flint, nearly plane on one side, while the other side was concave, with the same curvature as the crown glass. The process of grinding and polishing was now carried on in the usual manner. The tools are very simple-round plates of cast iron, about three feet in diameter, hollowed out to suit the curves of the lens. They have somewhat the appearance of huge shallow saucers, or more nearly still, |