336 



THE CIVIL ENGINELR AND ARCHITECTS JOURNAL. 



Nov. 



]n (he usual way, ;;ave the tlimensioDS as figured in the (liaerain. 

 sides of ibe excavulioD were to be fiuiijhed wilii stupes of 1 tu 1. 



Tlie 



Slope 



Ciilculiition of Volume. 



Heights at angles.. 15+ 5-r22+21 = fill. . Tab. No. 1 . 



Eiterior heights ..12+10+ 9+ H+ = 4.-> 

 23 + 22+21+21+23 = lit) 



18 + /1I + 23 = I'l 



10+15 + 21 = 19 



End$. 



l5^ 



24 ( 



as above.. 101728 



cubic yards 1071112 

 Slapcs at the angles. 

 Tab. No. 



15 Table 1. 

 24 

 5 

 22 



'A 



2-7778x15= 4l-f)(>7 



7 1111X24 = 170 066 



•3086X 5= 1 543 



5-9753x22 = 131 457 



0-8148 



1071-11 



345 333 



Total 10837-163 



It is to be observed that a more rigorous calculation, with the use of 

 Table 3, which would involve just double the number of figures, gives, as 

 the content of the slopes along the sides, a smaller quantity by G^ cube 

 yards, and of the slopes along the ends a smaller quantity by 42 cube yards 

 and if extreme accuracy is desired, such form of calculation must be fol- 

 lowed, as explained p. 17-19 of the introduction to my tables. It is only, 

 however, when each height did'ers from being an aritinelhical mean between 

 the two adjacent heights, that this more lengthened operation can be re- 

 quired J and such a diU'erence may be estimated by inspection, to enable the 

 calculator to judge whether it is desirable tu iucur the trouble. 



JouN Hughes, A. I. C. E. 



1 , Lancaster Place. 



" Sjnoe the tables are calculated to ftire ' lloth ■ sinpta of a cutliiig, tlie multiplier must 

 ba dIrUed by 2, io otftaiu the coDteuts uf * ou9 ' 8lO[je. 



A NEW MINING SURVEYING INSTRUMENT. 



Sir — I beg to offer to your notice, and through your valuable Journal 

 to that of practical surveyors and engineers, a sketch of a model instru- 

 ment for taking hori-«}ntal angles, which I think is new, and likely to be- 

 come exceedingly useful, although it is but a modification of the principle 

 upon which the quadrant and sextant are constructed. I have been led to 

 the construction of the model, by constant experience for the last 20 years, 

 of the difficulty and uncertainty of the use of the dial or compass for un- 

 derground surveying. Practical men need no mention of thise, but for 

 the information of those not actually conversant with subterraneous sur- 

 veying, I may mention briefly the principal difficulties, — there is first the 

 attraction of the needle by the tram rails (now generally composed of 

 wrought iron) which renders it necessary at each slation of the instrument, 

 to take them up for a distance (to make sure work) of 5 to 7 yards on each 

 side of it — a laborious operation, and much impeding the mining opera- 

 tions by obstructing the wagon-way, besides occupying much of the time 

 of the surveyor, who has to await the pulling np and removal of the rails. 

 The next difficulty is the slow but progressive variation of the needle ren- 

 dering a colliery plan of 9 or 10 years old altogether inaccurate, and there- 

 fore making it necessary to alter the meridians (generally numerous on a 

 working colliery plan) or to make allowances in the observations taking 

 during every survey made after the lapse of such a period of time. Then 

 follow local attractions in the stratum of the coal itself or in the strain 

 above or below it, often causing a difference of 2° to 3° between a fore and 

 a back observation on the same line. Another is the gradual weakening 

 of a needle in constant use, and its consequent sluggish working causing 

 great lo.ss of time, and great uncertainty — these are formidable evils, and 

 other minor ones might be adduced if necessary. 



It may be said with perfect truth that horizontal angles may be readily 

 taken by a common circumferentor, or by a theodolite, — but of these the 

 latter is too bulky, heavy, and complicated an instrument to be admissible 

 into or usable in a coal mine, under ordinary circumstances, and there is a 

 radical defect in the former which completely destroys its efficiency in 

 mine surveying. It consists in the instability of the instrument and its 

 consequent uncertainty during the movement of the upper up.)n the lower 

 limb, — and if by way of correcting this, the instrument be furnished with 

 a double set of sights, one for the back and tlie other for the fore observa- 

 tion, in the manner of those of early construction — this difficulty occurs, 

 that the surveyor having lixed one pair of sights, must go to the other side 

 of the instrument in a gallery very often less than three feet high, and than 

 five feet in width (and this width occupied by the legs and other parts of 

 the instrument itself) to take the other observation, and afterwards he 

 must go back again to take the first obseivatiou again to assure himself 

 Ihat the instrument has not shifted during the adjustment of the moveable 

 sights for the second observation. If he find, as is most probable, that it 

 has stirred, the observation must be repeated perhaps several times, and 

 this in a space where it is next to impossible to move without disturbing 

 the instrument. Even two operators, one on each side of it, would be use- 

 less, as they would be in the way in nine cases out often of each others 

 observation, and would obstruct it by intercepting the view of the object. 



By the instrument of which the above is a sketch, both objects are 

 brought to the eye, as by a quadraut, at the same vertical line, and seen at 

 the same time, and the angla indicated by the vernier, without any of the 



