874 SEC. 16. .GEOLOGY AND MINING. 



ment, working a circular plate with sights and vernier, for taking horizontal 

 angles. 3rd, a circular level, ground to a radius of about 15 feet, fitted inside 

 the dial on the base plate, in lieu of the usual cross levels outside. 4th, 

 fitted into the same case, with sockets screwed to receive three legs either 

 permanent or temporary, is a ball and socket stand, with adjusting rod which 

 enables the instrument to be correctly adjusted almost instantaneously, while 

 the parallel plates are in any position within 25 degrees of the perpendicular. 

 Where the ground to be surveyed is slippery, or the vein thin, with a low 

 roof, and its inclination steep, this arrangement of stand is of great advantage 

 to correct and rapid surveying. 



3397b. Davis's Improved Clinometer with tripod, which 

 folds up and forms a walking-stick. John Davis and Son. 



This clinometer is much used in geological surveys ; the arc being of a large 

 size, gives by aid of the levels the gradient of stratum very accurately. 



The special arrangement in this instrument is in the stand, also in the large 

 size of the compass, which turns over, rendering the clinometer capable of 

 doing the work of a level and dial approximately. Where great accuracy is 

 not required, it will save time and a more expensive instrument, and on 

 account of its extreme portability may be used when a level or dial could 

 not. Its outside dimensions are, when folded up, 6" by " by 3". 



3397c. Davis's Improved Hedley, Dial, or Circum- 

 ferentor, for mine surveying. John Davis and Son. 



This dial combines all the latest improvements of the best Hedley, with the 

 outside vernier of the theodolite. 



The figuring is so arranged that the readings of the needle and the vernier 

 tally, thus keeping one another in check. If the needle be used, the vernier 

 will detect the slightest local attraction. 



The Hedley sights and the vernier plate may be clamped, and the instru- 

 ment can then be used as an ordinary rigid dial. One great advantage of 

 this construction is that if the dial be out of adjustment, it is at once de- 

 tected by comparing the vernier and needle readings. 



The weight is not more than that of the ordinary Hedley, and it is equally 

 compact. 



3398. Frof. Junge's Levelling Staff for underground 

 use. The divisions are cut out of a brass plate and illuminated 

 by a sliding transparent glass screen placed in front of a candle, 

 so that the divisions appear as alternate light and dark bands of* 

 about an inch in breadth. 



Royal Saxon Mining Academy, Freiberg. 



3399. Collection of various Mine Signals for subterranean 

 measurement of angles with the theodolite. 



Royal Saxon Mining Academy, Freiberg. 



3400. Pocket Compass apparatus with stand. 



F. W. Breithaupt and Son, Cassel (G. Brcithaupt). 



3418. Photograph of a small Box Compass Apparatus. 



F. W. Breithaupt and Son, Cassel (G. Breithaupt). 



3401. Six-inch Theodolite, with two Telescopes, by Messrs. 

 Troughton & Simms, with adaptations for underground sur- 

 veying, suggested by the contributor. Walter Rowley, C.E. 



