. Transactions. Thorntons Surveying Dial-Circumferknt<»r. usual form. The semicircle is screwed to the outside of thecompass-box, and magnetic bearings are taken in the usualway. The instrument is mounted with a modified form ofHoffmans patent joint and with leveling-screws; and is some-times constructed without a circular compass, becoming thena very superior circumferentor, with a long trough magneticcompass below the horizontal circle, for determining the mag-netic meridian. 824 ADDITIONAL REMARKS ON SURVEYINO-INSTRUMENTS. Micron btbio Brough, in his further discus
. Transactions. Thorntons Surveying Dial-Circumferknt<»r. usual form. The semicircle is screwed to the outside of thecompass-box, and magnetic bearings are taken in the usualway. The instrument is mounted with a modified form ofHoffmans patent joint and with leveling-screws; and is some-times constructed without a circular compass, becoming thena very superior circumferentor, with a long trough magneticcompass below the horizontal circle, for determining the mag-netic meridian. 824 ADDITIONAL REMARKS ON SURVEYINO-INSTRUMENTS. Micron btbio Brough, in his further discussion,2 argues that neitherGascoigne (1639), Buygene (1659), Malvasia (1662), nor Au-zout and Picard(1667), contemplated the direct measurementof distances on the earth by means of the visual angle, withthe micrometer; an idea, however, clearly contemplated, in his Fia. Grubb-Davis Mine-Surveying Dial and Circumferentor. opinion, by Montanari in 1674, as well as later by James Wattin 1771, and William Green in 1778. But Townley, in 1667,distinctly says3 that Gascoigne had, before our late Civil Wars,. . for some Years made use of it [his instrument] not onlyfor taking the Diameter of the Planets and Distances upon 2 Trans., xxxiii., 1037. 3 Trans., xxxi., 26, and Phil. Trans., No. 25, p. 457 (May, 1667). \M»I PIONAL kim LRKfi OS 81 i:\ BT1 BTO in- PR1 KEN Land, but, etc. This evidenoe Beems to establish the Getcf thaiGascoigne was the first English inventor and user of a microm-eter eye-piece, and consequently of a tacheometric and Btadia-metric principle, for finding distances upon laud. The onlypertinent and effective contradiction fit would be the demon-stration that Townley was mistaken in his statement. allude- to ill* death of Gascoigne at Marston Moor(1644), and says that he was then 28 years old. In L6therefore (when Town
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