A USEFUL INVENTION.

Evening Star, Issue 2991, 19 September 1872, Page 4

A USEFUL INVENTION.

A means of correcting errors due to the variation of the needle, has always been desired by surveyors, Mr John Phillips, C.E., Master of the Ballarat School of Mines, who has been experimenting that way for the last thirty years, has invented some additions to the ordinary instruments in use, and his new instrument, which is, so to speak, the mechanical resultant of his practice, he calls “The Polyscopic Compass.” It is an instrument for assigning exact magnetic bearing to the surveyor’s base lines, and the true magnetic variations, for observing with precision the fluctuations of the magnetic course from hour to hour, and generally is adapted for use as a circumferentor. Its readings are to minutes, and there is no limit to its number of independent reading for averaging and for verification. Mr Phillips claims for his instrument five novel means of overcoming the sources of error incident to the ordinary circumferentor. We will give them in order ;—The mode of attachment is such that there is no laxity or vibration in the apparatus ; there are eighteen instruments in one, or eighteen sights or sight-ways ; the needle is readily inverted ; the needle is relieved of friction at the pivot; the agate at the pivot is easily shifted. All these are matters which the professional man will at once understand. Mr Phillips informs us that both Mr Ellery, the astronomer, and the Surveyor-General, have spoken favorably of instrument. The cost, with a plain compass, is LIG ; with microscope, L 18; with verniers, L2U; theodolite, with telescope instead of plain sights, L 24 ; theodolite, combined with double telescope, L29. —BaVarut Miner.