This will be composed of a conduction and a convection current, the latter due to rising or falling air currents carrying ions.
The object of all heating apparatus is the transference of heat from the fire to the various parts of the building it is intended to warm, and this transfer may be effected by radiation, by conduction or by convection.
In ordinary cases conduction and convection suffice to dissipate the heat generated by the brake, but when a great deal of lowering has to be rapidly performed, or heavy loads have to be lowered to a great depth, special arrangements have to be provided.
This method of communication by magnetic induction through space establishes, therefore, a second method of wireless telegraphy which is quite independent of and different from that due to conduction through earth or water.
The method of induction between insulated primary and secondary circuits laid out flat on the surface of the earth proves to be of limited application, and in his later experiments Preece returned to a method which unites both conduction and induction as the means of affecting one circuit by a current in another.
On the question of how far the effects are due to conduction between the earth plates, and how far to true electromagnetic induction, authorities differ, some being of opinion that the two effects are in operation together.
The electromotive force of the coil is, however, great enough to create in these air gaps displacement currents which are of magnitude sufficient to be equivalent to the conduction current required to actuate a telephone.
Simple pits (p.) enable conduction to take place readily from one to another.
In the stalk of the sporogonium there is a similar strand, which is of course not in direct connection with, but continues the conduction of water from, the strand of the gametophytic axis.
Wood thus altered is known as heart-wood, or duramen, as distinguished from the young sap-wood, or alburnum, which, forming a cylinder next the cambium, remains alive and carries on the active functions of the xylem, particularly the conduction of water.
The increasing development of the wood as the tree grows older is largely due to the demands for the conduction of water and mineral matters dissolved in it, which are made by the increased number of leaves which from year to year it bears, and which must each be put into communication with the central mass by the formation of new vascular bundles.
If we eliminate the reverse electromotive forces of polarization at the two electrodes, the conduction of electricity through electrolytes is found to conform to Ohm's law; that is, once the polarization is overcome, the current is proportional to the electromotive force applied to the bulk of the liquid.
Kohlrausch formulated a theory of electrolytic conduction based on the idea that, under the action of the electric forces, the oppositely charged ions moved in opposite directions through the liquid, carrying their charges with them.
On the view of the process of conduction described above, the amount of electricity conveyed per second is measured by the product of the number of ions, known from the concentration of the solution, the charge carried by each of them, and the velocity with which, on the average, they move through the liquid.
The details of the calculation are given in the article Electric conduction, § where also will be found an account of the methods which have been used to measure the velocities of many ions by direct visual observation.
But not only has it explained satisfactorily the electrical properties of solutions, but it seems to be the only known hypothesis which is consistent with the experimental relation between the concentration of a solution and its electrical conductivity (see Electric conduction, Brit.
The interpretation of the phenomena of gaseous conduction was rendered possible by the knowledge previously acquired of conduction through liquids; the newer subject is now reaching a position whence it can repay its debt to the older.
Thomson has shown (see CONDUCTION, ELECTRIC, § III.) that the negative ions in certain cases of gaseous conduction are much more mobile than the corresponding positive ions, and possess a mass of about the one-thousandth part of that of a hydrogen atom.
Some of the more important papers on the subject have been reprinted for Harper's Series of Scientific Memoirs in Electrolytic Conduction (1899) and the Modern Theory of Solution (1899).
Conductivity.-Conductivity, whether thermic or electric, is very differently developed in different metals; and, as an exact knowledge of these conductivities is of great importance, much attention has been given to their numerical determination (see Electric conduction; and Conduction Of Heat).
In starting the furnace, the bottom is prepared by ramming it with charcoal-powder that has been soaked in milk of lime and dried, so that each particle is coated with a film of lime, which serves to reduce the loss of current by conduction through the lining when the furnace becomes hot.
Towards the end of his life he was occupied with experimental inquiries into the laws of the conduction of heat in bars, and his last piece of work was to show that the thermal conductivity of iron diminishes with increase of temperature.
If heat passes " of itself " from a higher to a lower temperature by conduction, convection or radiation, the transfer cannot be reversed without an expenditure of work.
Conduction has practically no effect, for the coefficient of thermal conductivity in sea-water is so small that if a mass of sea-water were cooled to 0° C. and the surface kept at a temperature of 30° C., 6 months would elapse before a temperature of 15° C. was reached at the depth of 1 3 metres, 1 year at 1 85 metres, and io years at 5.8 metres.
Here we have an instance of the conduction of heat.
His most important work was concerned with the conduction of heat and with spectroscopy.