For heavy gradients rope haulage has no rival, though for moderate grades it is often advantageously replaced by electric and compressed air haulage.
The difference of the temperature gradients D/l at the ends of the section was simultaneously obtained from the difference D of the readings of a pair of couples at either end connected in opposition.
At Such Times Gradients Of 400 Or 500 Volts Per Metre Are By No Means Unusual At Kew, And Voltages Of 700 Or Boo Are Occasionally Met With.
If the mean of the gradients observed at the ground and at 1500 metres be taken as an approximation to the mean value of the gradient throughout the lowest 1500 metres of the atmosphere, we find for the potential at 1500 metres level 112,500 volts.
The trains are few and the speed on all these lines is moderate, but the gradients are often very heavy.
The chemical characters of the well-waters, the irregular distribution of the water-pressure, the distribution of the underground thermal gradients, and the occurrence in some of the wells of a tidal rise and fall of a varying period, are facts which are not explained on the simple hydrostatic theory.
As far as Terracina it ran in an almost entirely straight line, even through the Alban Hills, where the gradients are steep.
At the same time, as the gradients are gradually increasing on account of the upheaval of the continent, the rivers dig their channels deeper and deeper.
Before that time the St Paul had been a great local railway, operating primarily in the Dakotas, Minnesota, Iowa, Wisconsin and Illinois; but by the construction of a long arm from the Missouri river to Spokane, Seattle and Tacoma, it became a transcontinental line of the first importance, avoiding the mistakes of earlier railway builders by securing a line with easy gradients through the most favourable regions.
In the second place, except in the unlikely event of all the places on the selected route lying at the same elevation, a line that is perfectly level is a physical impossibility; and from engineering considerations, even one with uniform gradients will be impracticable on the score of cost, unless the surface of the country is extraordinarily even.
Other things being equal, that route is best which will serve the district most conveniently and secure the highest revenue; and the most favourable combination of curves and gradients is that by which the annual cost of conveying the traffic which the line will be called on to carry, added to the annual interest on the capital expended in construction, will be made a minimum.
One of the steepest gradients in England on an important line is the Lickey incline at Bromsgrove, on the Midland railway between Birmingham and Gloucester, where the slope is 1 in 37 for two miles.
In practice the gradient should not exceed i in 221, and even that is too steep, since theoretical conditions cannot always be realized; a wet rail will reduce the adhesion, and the gradients must be such that some paying load can be hauled in all weathers.
When an engineer has to construct a railway up a hill having a still steeper slope, he must secure practicable gradients by laying out the line in ascending spirals, if necessary tunnelling into the hill, as on the St Gothard railway, or in a series of zigzags, or he must resort to a rack or a cable railway.
Racks of this type usually become impracticable for gradients steeper than 1 in 4, partly because of the excessive weight of the engine required and partly because of the tendency of the cog-wheel to mount the rack.
- Gradients are measured either by stating the number of feet horizontally, G say, in which the vertical rise is I ft., or by the vertical rise in too ft.
In the great continental basin there are long lines with easy gradients and curves, while in the Allegheny and Rocky Mountains the gradients are stiff, and the curves numerous and of short radius.
This system has the advantage of the greatest convenience in operation, no lifts being required, since the distance from the street surface to the station platform is about 12 to 15 ft.; it has the disadvantages, however, of necessitating the tearing up of the street surface during construction, and the readjustment of sewer, water, gas and electric mains and other subsurface structures, and of having the gradients partially dependent on the surface topography.
Thus the gauge may be narrow, the line single, the rails lighter than those used in standard practice, while deep cuttings and high embankments may be avoided by permitting the curves to be sharper and the gradients steeper: such points conduce to cheapness of construction.
An hour on long inclines with gradients steeper than i in 50, and also on a line which had scarcely any straight portions and in which there were many curves of 600 ft.
Radius and gradients of 1 in 50.
Except in special cases, gradients must not exceed 3 in moo; and between gradients in the opposite sense there must be not less than 60 metres of level for 1.44 m.
There are gradients of I in 20 and I in 25.
As might be expected in a country possessing the physical features of Natal, the gradients and curves are exceptionally severe.
The Orange Free State line, after leaving Ladysmith, ascends by steep gradients the whole of its own course in Natal territory, and when it gains the summit at Van Reenen's Pass it is 5500 ft.
(For details see Hughes, Text-book of Coal Mining, pp. 236-272; Hildenbrand, Underground Haulage by Wire Rope.) Rope haulage is widely used in collieries, and sometimes in other mines having large lateral extent and heavy traffic. With the tail-rope system, cars are run in long trains at high speed, curves and branches are easily worked, and gradients may be steep, though undulating gradients are somewhat disadvantageous.
Their situation was unsatisfactory not only in the tactical sense, but also from the point of view of keeping the troops supplied, owing to their being perched on ridges with steep gradients behind them.
Such gradients are of a truly mountainous character, the angle of slope from the Eibsee to the Zugspitze is 30°, and that from Alpiglen station to the summit of the Eiger is 42°.
This system presents the greatest advantages in point of economy of driving power, especially where the gradients are variable, but is expensive in first cost, and is not well suited for curves, and branch roads cannot be worked continuously, as a fresh set of pulleys worked by bevel gearing is required for each branch.
The larger streams have cut their channels to very moderate gradients, but the smaller ones are steeper.
In the midwinter month, it is the eastern half of the country that has strong temperature contrasts; the temperature gradients are twice as strong between New Orleans and Minneapolis as on the Pacific coast, and the contrast between Jacksonville, Fla., and Eastport, Me., is about the same as between San Diego, Cal., and the Aleutian Islands.
But thislinvolves an assumption, undoubtedly true for small temperature-gradients, but still an assumption, viz.
Of that distance being at gradients of 1 in 40 to 1 in 45.
Attention has been called to the fact that the bare rocks and steep gradients which are common in the Western Division allow of the heavy rainfall running off the surface rapidly, while the flat and often clayey lands of the Eastern Division retain the scantier rainfall in the soil for a longer time, so that for agricultural purposes the effect of the rainfall is not very dissimilar throughout the country.
These gradients enable the inconstant streams tributary to the Colorado to carve their canyons, some of which are in themselves very remarkable, though insignificant beside the Grand Canyon.
On the southern or Indian side the routes to Tibet and Ladakh follow the levels of Himalayan valleys with no remarkably steep gradients till they near the approach to the water-divide.
The dominant mountain system of Afghanistan is the Hindu Kush, and that extension westwards of its water-divide which is indicated by the Koh-i-Baba to the north-west of Kabul, and by the Firozkhoi plateau (Karjistan), which merges still farther to the west by gentle gradients into the Paropamisus, and which may be traced across the Hari Rud to Mashad.
This agreement was a very satisfactory test of the accuracy of the fundamental law of conduction, as the gradients and periods varied so widely in the two cases.
One of the steepest gradients in England over such a distance.
(3) Resistance due to gradients, represented by R9.