connected with Astronomical Physics. 269 



•of climate at the polar and equatorial regions respectively of 

 our earth. The citing of geological evidence as to past 

 glaciation in the tropics, has not escaped some ridicule. 

 And this phase of its life-history the planet Uranus seems to 

 be traversing at the present moment; its pole or rather its 

 axis resting in practical coincidence with the ecliptic or with 

 the plane of its orbit (a fact hitherto apparently regarded as 

 an enigma). 



And if solar tidal-action be a persistent potent reality, such 

 a vera causa for the production of effects, distiDctly observable 

 in time (as concerns our own system), cannot be passed over 

 with propriety. For Astronomy to neglect the legitimate 

 deductions dependent on the demonstrably penetrable time- 

 epoch in the past, would be a procedure by which some 

 physical deductions of value may be missed. 



The putting of statistical results into a shape suited to 

 facile conception may requite a thought or two. Thus to 

 refer for a moment to a point alluded to in my last commu- 

 nication to the Philosophical Magazine for December 1906. 

 By reduction of the value of the gravitational pressure 

 (superincumbent) at the centre of the earth to that existing 

 on a unit of surface taken adequately small, (say) one 

 square millimetre, the value of the pressure (conveniently 

 referred by Prof. See to that of the mercury in a barometric 

 column of computed length = 2383*152 kilometres) comes 

 out as equal to 32 tonnes (32 tons, English, about) per square 

 millimetre of surface-area, at centre of our globe. It becomes 

 obvious that solids would " flow" together like liquids under 

 a stress* of this intensity, otherwise represented by a pressure 

 of upwards of three million kilogrammes per square centi- 

 metre, or 20,000 tons per square inch. 



It is considered certain that our satellite at one time 

 rotated more quickly than a single revolution per month on 

 its axis. If so, the lunar globe must once have been more 

 flattened at the poles than now. In the resulting eventual 

 diminution of this primordial oblateness of shape, by slow re- 

 adjustment under gravitational and (changing) centrifugal 

 stress, spread over a lengthy epoch, the polar regions of our 

 Moon would naturally have receded somewhat (virtually 7 N 

 outwards, — possibly throwing some light on the curious ra- 

 diating or starred marks (resembling fissures, called "rays"), 

 discernible even with a small telescope, in the vicinity 

 especially of one pole of our satellite. 



* In passing, two previous papers of mine may be referred to : in 

 ' Nature/ March 30, 1879, and Philosophical Magazine, August 1879, 

 .as having some bearing, direct or indirect, on the meteoritic theory of 

 planetary evolution. 



