294 SCIENTIFIC APPARATUS. 



possible in some cases to employ such as also serve for surface 

 surveys, but the requirements of mines in general are such as need 

 a difference of arrangement, especially with a view to portability, 

 and to their being used in narrow or low and tortuous places. 

 M. Combes, the late Professor at the Ecole des Mines, devised a 

 theodolite for underground work, fitted with a telescope attached 

 to a vertical graduated circle for giving the inclinations ; and 

 modifications have been made on this, as notably in the excentric 

 theodolite of Messrs. Stackpole of New York, recently described by 

 Professor Vinter, of Columbia College. An important advantage 

 connected with this arrangement is, that we may thus measure any 

 and all vertical angles without being interfered with by the hori- 

 zontal limb corrections of course having to be applied for the 

 eccentricity. 



The method of supporting the axis of the telescope, like that of 

 a transit instrument, has also been applied underground, as in the 

 transit theodolite of Mr. H. D. Hoskold,* and in the instruments 

 much used in the United States under the term of the engineers' 

 transit. Those made by Heller and Brightly of Philadelphia are 

 described by Professor R. W. Raymond as excellent transits, 

 weighing only 5*lbs., exclusive of the tripod of 3ilbs. The needle 

 is three inches long, and the ring divided to half degrees. A 

 convenient form of plummet lamp is adapted to use with the same 

 instruments, to read off after either sighting upon the strings to 

 which such lamps are suspended, or on bisecting the flame. 



It should be added that many good surveys, particularly those 

 of limited areas, are still executed with the miner's dial, and that 

 it is generally recognised that better results are to be had from a 

 rough instrument in practised hands, than from a superior one 

 less skilfully employed. The old suspension-compass has many 

 adherents, and Adolf Plaminek t proposes a new form of it, in 



* "A Treatise on Mining and Surveying." H. D. Hoskold. London: 

 Atchley and Co., 1863. 



f Berg-und Hiittenmiinnisches Jahrbuch, bd. xxii. Wien, 1874. 



