Tables of Heights in Sind, the Punjab, N.W. Provinces and Central India, Determined by the Great Trigonometrical Survey of India, Trigonometrically and by Spirit Leveling Operations to May 1862

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Public Works Department Press, 1863 - 196 pages
 

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Page 23 - ... in certain lights its extremities may be taken for the ends of the bubble. When light falls obliquely on the instrument, the outer edge of the rim towards the light is more •clearly defined than the inner, while at the opposite end of the bubble the inner edge is most clearly defined. Hence there...
Page 13 - ... amount, which could only have been detected by the second and independent series of levels, taken over the ground in an opposite direction. For this reason alone, I should not consider it safe to depend on one course of levels only, whatever may have been the precautions used to guard against error. The total length of my line of leveling between Portishead and Axmouth, besides the branch lines to Bristol and East Quantockshead, is about 74 miles. This distance was divided into separate stages;...
Page 13 - The error consists in this;—that in proceeding with the leveling •operation along a line which is really level, the further end constantly appears, from the observation, to be the lower end ; and the amount of this depression appears to increase with the distance. Hence, when we go to the end of a line and then return to the starting point, we find the resulting elevation of the point lower than its real elevation. The difference arising from this cause is never considerable, but is always in...
Page 23 - ... ends of the bubble. When light falls obliquely on the instrument, the outer edge of the rim, towards the light, is more clearly defined than the inner, while at the opposite end of the bubble, the inner edge of the rim is most clearly defined ; hence there is a tendency to bring the bubble too much towards the light, and to give the readings an erroneous bias by an amount equal to half the breadth of the rim, which might have a considerable effect on a long line of levels.
Page 14 - ... lower when I returned, than it was at my setting out. But as the height of this point is the same in both cases, the error must, of course, be thrown on the distant point, or station at which the returning levels commenced, which reverses the first apparent differences, and makes all the heights in the second series progressively greater than those in the first, the most distant point having the greatest error. The following table gives the differences thus found at...
Page 23 - ... staff-reading are again likely to cancel themselves, except perhaps in working in a meridional direction, when, one staff being invariably more illuminated than the other, these errors become cumulative. The most probable source of personal error is in reading the bubble. The observer generally gets a side view of the bubble refracted obliquely through the thickness of the glass tube, which is not so clear as the view from above. The rim round the bubble caused by the adhesion of the liquid to...
Page 14 - The following table gives the differences thus found at iJO points along the line between Portishead and Axmouth, the height, in every instance, coming out greater from the series of levels returning towards Portishead. No. of Station Miles from Height greater by in Minute-book. Portishead. 2nd than 1st Levels. Feet. 1683 .... 0 .... O'OOOO 1631 .... 3 .... 0-063.3 1593 .... 6 .... 0-1557 1562 .... 9 .... 0-2/03 No.
Page 95 - ... seventy feet ; length of adit, two hundred and sixty feet. Cost of adit, $5,320 ; cost of shaft, $1,260. Strike of lode, N. 30° E. ; dip 40° W. ; power, twelve feet. Walls of lode, talcose schist ; ores, pyriferous and gossan. McGHEE, Director. EXPERIMENTAL MINE, COLUMBIA, TUOLUMNE COUNTY. This mine is situated about one and a half miles north of the town of Columbia, in the County of Tuolumne. It was first located in 1852, and some little money and labor expended upon it sufficient to fairly...
Page 1 - Commissioners represented that it was frequently found very difficult to form a correct opinion as to the merits of existing or proposed works for drainage or water supply, on account of the absence of complete and systematic sets of levels for each Station.
Page 14 - ... returning upon any part of it ; it being much more probable that errors depending on the state of the atmosphere will balance each other in the former than in the latter case. My own experience, therefore, leads to the conclusion, that no levelling can be expected to give a correct result, unless it be performed in opposite directions, and the mean of both results be taken ; instead of depending, as Captain Lloyd appears to have done, on the consistency of separate sets of successive readings.

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