HISTORY OF PHYSICAL ASTRONOMY.

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says:—“ Could I purchase it with travel, or procure it for gold, I wouldnot be without a telescope for observing small angles in the heavens;nor want the use of your other device of a glass in a cane upon the move-able ruler of your sextant, as I remember, for helping to the exact pointof the sun’s rays.”*

The perusal of the foregoing extracts cannot leave a shadow of a doubtin the mind of the reader that Gascoigne distinctly perceived the advan-tage of telescopic sights in fixing the position of a celestial body, and thathe had actually reduced his ideas to practice, in making observations withthe quadrant and the sextant. To him, therefore, must be awarded thecredit due to the original invention of this important method of observa-tion. It has been already remarked that the application of the Galileantelescope to that purpose was impracticable. The above-cited extractsfrom Gascoigne’s letters clearly prove that he had succeeded in fixing theposition of the optical axis of his telescope, and in this respect they tendto corroborate the assertion of Sherburne that he was the first who con-structed a telescope composed of two convex lenses.

The materials which serve to establish the interesting fact that Gas-coigne employed telescopic sights in observing the celestial bodies, werenot published until early in the beginning of the eighteenth century, whenthe same mode of observation had been already known to astronomers forabout fifty years. The improvement which he thus effected can onlybe regarded, therefore, as forming the groundwork of an interestingepisode in the history of practical astronomy, rather than as constitutinga link in the chain of gradual advancement. In this respect it differsfrom his invention of the micrometer, which continued after his deathto be made use of in the north of England, although it appears to havebeen unknown for many years both in London and on the Gontinent.

The earliest allusion to the use of the telescope in observing the posi-tions of the celestial bodies is contained in Sprat’s “ History of theRoyal Society.” In a general exposition of the labours of the Society, towhich reference has already been made, he makes the following statement:“ They (the Fellows of the Society) have suggested the making of a per-fect survey, map, and tables of all the fixed stars within the zodiac, bothvisible to the naked eye and discoverable by a six-foot telescope with alarge aperture; towards the observing the apparent places of the planetswith a telescope both by sea and land. This has been approved andbegun, several of the Fellows having their portions of the heavens allot-ted to them.”-)

* The following extracts from the same collection of letters exhibit a beautiful illus-tration of the feeling which ought to reign between persons engaged in scientific pursuits,whether during the period of youthful enthusiasm or that of mature manhood. In a letterto Gascoigne, dated December 8, 1640, Crabtree thus writes:—“ My friend, Mr. Hor-rocks, professeth that little touch which I gave him of your inventions, hath ravished hismind quite from itself, and left him in an extasie between admiration and amazement. Ibeseech you, sir, slack not your intentions for the perfecting of your begun wonders.We travel with desire till we bear of your full delivery. You have our votes, our hearts,and our hands should not be wanting if we could further you.” In another letter datedDecember 6, 1641, he thus writes to Gascoigne :—“ No man that hath written of thediagram (of Hipparchus ) understood it fully or described it rightly, but only Kepler andour Horrocks, for whose immature death there is yet scarce a day which I pass withoutsome pang of sorrow.”

+ Sprat’s “History of the Royal Society,” p. 190. The close resemblance of thisproject to that in which the Berlin Academy of Sciences is engaged in. the present day,cannot fail to strike the reader.