This will be composed of a conduction and a convection current, the latter due to rising or falling air currents carrying ions.
This gives a convection current of 2.7 X108 electrostatic units, or about 1/27 of the conduction current.
Gerdien's estimate of the convection current is for fine weather conditions.
Wilson considers that convection currents in the upper atmosphere would be quite inadequate, but conduction may, he thinks, be sufficient alone.
A closed stove acts mainly by convection; though when heated to a high temperature it gives out radiant heat.
The nearly vertical vanes is balanced by the convection currents.
The penetration of warmth from the surface is effected by direct radiation, and by convection by particles rendered dense by evaporation increasing salinity.
In other enclosed seas which are shut off from the ocean by a very shallow sill the rule holds good that the homothermic water below the level of the sill is at the lowest temperature reached by the surface water in the coldest season of the year, provided always that the stratification of salinity is such as to permit of convection being set up. To this group belongs the Arctic Sea; the Norwegian Sea is homothermic below J50 fathoms at 29.8° F., but this cold water does not penetrate into the Arctic Basin on account of the ridge between Spitsbergen and Greenland, and there the water below 1400 fathoms has a temperature of 30 6° to 30.7° F.
Because the surface layers of water are too light, on account of the low salinity due to ice-melting, to enable even the cold of a polar winter to set up a downward convection current.
Before 1868 Maxwell conducted the experiment by sending light from the illuminated cross-wires of an observing telescope forward through the object-glass, and through a train of prisms, and then reflecting it back along the same path; any influence of convection would conspire in altering both refractions, but yet no displacement of the image depending on the earth's motion was detected.
As will be seen later, modern experiments have confirmed the entire absence of any effect, such as convection would produce, to very high precision.
These conditions cannot be consistent with sensible convection of the aether near the earth without involving discontinuity in its motion at some intermediate distance, so that we are thrown back on the previous theory.
The convection of a medium thus polarized involves electric disturbance, and therefore must contribute to the true electric current; the determination of this constituent of the current is the most delicate point in the investigation.
The establishment and convection of a single polar atom constitutes in fact a quasi-magnetization, in addition to the polarization current as above defined, the negative poles completing the current circuits of the positive ones.
1 On subtracting from this total the current of establishment of polarization d/dtl (f',g',h) as formulated above, there remains vd/dx(f',g',h) as the current of convection of polarization when the convection is taken for simplicity to be in the direction of the axis of x with velocity v.
The polarization itself is determined from the electric force (P,Q,R) by the usual statical formula of linear type which becomes tor an isotropic medium (.f',g',h') = c2(P,Q,R), because any change of the dielectric constant K arising from the convection of the material through the aether must be independent of the sign of v and therefore be of the second order.
It ascends the flow pipe by convection, where its onward journey would speedily end if it were not for the driving force of other molecules of water following, and the suction set up by the gravitation into the boiler of the cooled water by the return pipe.
In measuring conduction of heat in fluids, it is possible to some extent to eliminate the effects of molar convection or mixing, but it would not be possible to distinguish between diffusion, or internal radiation, and conduction.
The conductivity probably changes with temperature in the same way, being proportional to the product of the viscosity and the specific heat; but the experimental investigation presents difficulties on account of the necessity of eliminating the effects of radiation and convection, and the results of different observers often differ considerably from theory and from each other.
It is not difficult in such compact species to distinguish between superficial cells, whose chief function is assimilation, subjacent cells charged with reserve material, and a core of tissue engaged in the convection of elaborated material from part to part.
The coefficient of heating of a calorimeter when it is below the temperature of its surroundings is seldom, if ever, the same as the coefficient of cooling at the higher temperature, since the convection currents, which do most of the heating or cooling, are rarely symmetrical in the two cases, and moreover, the duration of the two stages is seldom the same.
The surface of the calorimeter and the enclosure should be permanently blackened so as to increase the loss of heat by radiation as much as possible, as compared with the losses by convection and conduction, which are less regular.
In the vast majority of cases the bacilli are in the lymphatic or the circulatory system, and aerial convection, even for a short distance, seems highly improbable.
Since the only cause for these convection currents is the statical instability produced by radiation, and the rapid stifling of radiations within the body produces there a temperature gradient falling very slowly, they would be for the most part extremely slight.
Indeed it seems that, in the final distribution of density throughout the part which is not subject to violent convection currents, it must increase slightly from the centre outwards, since the currents would cease altogether as soon as 'a uniform state was restored.
In these waters a vertical circulation is kept up by convection 287 currents.