## A Treatise on Topography: In which the Science and Practical Detail of Trigonometrical Surveying are Explained, Volume 1 |

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accuracy altitude arc passed axis of rotation azimuth barometer barometrical formula bubble calculation centre chord co-efficient column of mercury conical surface correction Cotang D.M. Tang degrees of Fahrenheit's denoted density difference of level direction division earth ellipticity equal equation error example expressed extremities Fahrenheit's Thermometer formula freezing Point geodesic operations give H sec heavenly body height horary angle horizon inclination instrument large mirror latitude limb logarithms longitude lower station means measured mercury meridian number of observations observed angle obtained optic axis perpendicular plane plumb line position preceding quantity radius ratio reduced reflecting circle refraction repeating circle repelling screws second term sexagesimal sextant side small mirror spherical excess spherical triangle star strata stratum subtracted sufficient supposed surface tance temperature terrestrial object tion tube upper telescope vertical line yards zenith distances

### Popular passages

Page 167 - ... barometer, observed at each of them. Newton, in his Principia, perfected that theory by showing what regard was to be paid to the diminution of the gravity of the molecules of air, according as the distance from the surface of the earth increased.. But, what is very remarkable in so scrupulous an observer of nature, he omitted also to consider the effect of the variations of heat, and of the progressive decrease of the temperature on the density of the beds of air. At this time observations of...

Page 176 - The same relation will subsist in passing from the second stratum to the third, from the third to the fourth, and so on in successsion, at least on the suppositions that have been admitted ; so that we shall have the following equations.

Page 199 - From the foregoing statements it may be safely inferred that " the mean height of the barometer at the level of the sea being the same in every part of the globe...

Page 195 - T, the temperature of the barometer. ( t, the temperature of the air. !A', the height of the barometer. T', the temperature of the barometer. t', the temperature of the air. Represent by s the height of the lower station above the level of the sea, by L the latitude of the place, and by h the observed height, h', reduced to the temperature T.

Page 183 - F the elastic force of the aqueous vapour con* tained in it, that is, the part of the barometrical pressure which the vapour sustains. The total' weight of the bed may be considered as composed of two parts ; viz. of a certain quantity of vapour, the elastic force of which is F, and of a certain quantity of dry atmospheric air, the elasticity of which is H — F; let p be the whole weight of the bed, if it were entirely composed of dry air, under a pressure H. The weight of the same...

Page 72 - During this operation, the lower telescope should always remain fixed upon the object on the right ; if it does not, it may be brought to it by means of the drum screw, and the superior telescope directed again to the centre. This should be repeated two or three times, and the mean of the results betaken.

Page 92 - ... if from each of its angles one-third of the excess of the sum of its three angles above two right angles be subtracted, the angles so diminished may be taken for the angles of a rectilinear triangle, the sides of -which are equal in length to those of the proposed spherical triangle" The demonstration of this rule will be given in.

Page 182 - According to the experiments of Saussure and Watt, the weight of this vapour is to that of air as 10 to 14, when their temperatures and...

Page 180 - The co-efficient C, which expresses the ratio of the density to the height of the barometrical column, ought therefore to vary in the same proportion, and consequently it will become C (1 —0.002837. cos. 2 4-), which being substituted in the value of X, gives x_ M 7 ~ C ( 1 — 0.002837.

Page 128 - ... first, that we have the equation of the surface of the spheroid of revolution ; then by referring that surface to co-ordinates taken in the cutting plane, we shall obtain an equation between two indeterminate quantities only, and we shall thus have the equation of the curve made by the intersection. To find the equation of a spheroid generated by the revolution of an ellipse about its shorter axis, it must be considered that the generating curve being plane, its equations will be...