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MR. J. J. WATERSTON OR THE PHYSICS OF MEDIA COMPOSED OF 
The less this ratio, the more exact, of course, is this method of estimating heights, 
and it depends greatly on the value of the constant H (see Note B), for the less the 
inclination of the line of vapour is to the axis the smaller is the height that 
corresponds to a difference of 1° in the boiling point. For mercury this is only 
248 feet, but the temperature is inconveniently high. 
Pure sulphuric ether appears to be the best adapted, as its boiling temperature is 
low, and the disadvantage of the great amount of the difference of elevation for 1" 
might, perhaps, be compensated for, by employing a very delicate alcohol thermometer, 
with the divisions of the scale large and extending only from 60° to 100°. The ether 
need not have access to the air; the equilibrium of pressure may be indicated by the 
rising of a thin metallic capsule air-tight and elastic. 
Such an instrument would require little more than the heat of the hand to bring it 
into action, and perhaps might be made sufficiently delicate to be used as a machine 
for taking levels and making sections of a country. 
Note K.—Central Heat. 
It is not difficult to compute the temperature that the atmosphere would have if it 
were supposed to be continued through a shaft to the centre of the earth. Suppose 
the force of gravity to diminish with the central radius, which is the case in a 
homogeneous sphere, the temperature of the air at the centre would be about 29,000°, 
and the density much greater than that of any known solid. 
Heat, if it is motion, cannot be propagated upwards without loss or conducted 
downwards without gain, any more than can a body when projected upw T ards retain 
its original velocity without diminution, or when projected downwards without 
increase. 
The temperature in mines (according to M. Cordier) increases in descending at the 
rate of 1° to 50 or 60 feet. Is this the natural condition of vertical equilibrium of 
molecular vis viva within the crust of the globe ? If such were the case some regular 
difference might be found between the top and bottom temperatures in pillars or 
lofty buildings if precautions could be taken to prevent horizontal conduction. 
Note L.—Nebular Hypothesis. 
The vis viva theory appears to harmonize well with the Nebular Hypothesis of 
Laplace. The intense activity of the molecules of the Sun’s mass may be viewed 
as the result of, or to have been originally produced by, its centripetal force while 
condensing. The motion generated is not lost, as it is in appearance when inelastic 
bodies meet each other with equal momenta. The clashing together of the descending- 
elastic matter is followed by equal recoil in the opposite direction, and molecular 
vis viva is generated. We see this take place on a minute scale when metals are 
