TRANSACTIONS OF SECTION A. 485 



think, preserved them as a standing memorial of the primitive period of rotation of 

 that planet. The Uranian system, on the other hand, appears, at least at first sight, 

 a stumbling-hlock. 



It is easy to discern in the planetary system many vera causae, which tend to 

 change its configuration ; but it is in general very hard to give any quantitative 

 estimate of their effects. 



It will have been seen that, in the investigation of which I have given an im- 

 perfect account, free scope has been given to speculation, but that speculation has 

 been governed and directed in every case by appeal to the numerical results of a 

 dynamical problem, and I therefore submit that it stands on a different footing from 

 the numerous general speculations to which the nebular hypothesis has given rise. 



9. On the Limits of Hypotheses regarding the Physical Properties of the Matter 

 of the Interior of the Earth. By Professor Henry Hennesst, F.E.S. 



The author pointed out that every hypothesis of a philosophical character must 

 conform to the condition of not being in contradiction to observed facts. The known 

 physical properties of solids, liquids, and gases were referred to, and the bearings 

 of such properties on the problems regarding the earth's structure were indicated. 

 Mathematical inquiries, which started from supposing an incompressible liquid en- 

 closed in a compressible and elastic envelope, could not lead to conclusions at all 

 invalidating the opinion held by the author. He supported his views by deductions 

 drawn from the observed properties of solids and liquids, and not from hypotheses 

 of unreal and impossible properties of these substances such as formed the basis of 

 the elaborate and learned mathematical labours of Sir William Thomson and 

 Mr. Darwin. The views he had long since maintained in opposition to the con- 

 clusions of the late Mr. Hopkins regarding the earth's solidity had been discussed 

 in a manner satisfactory to the author in the Academy of Sciences of Paris,* when 

 he had formally laid his views before that scientific body, and his subsequent 

 studies had led him to maintain the correctness of his original views respecting the 

 earth's internal fluidity .f 



10. On the Climate of the British Islands. 

 By Professor Henry Hennessy, F.R.S. 



The author laid before the Section the results of- the discussion on temperature 

 observations made at a great many stations in Great Britain and Ireland tabulated 

 in isothermal groups. He pointed out the lines of equal temperature over the 

 British Isles deduced from these observations conformed to the same general law 

 as that which he had communicated to the Association at former meetings — namely, 

 that the isothermal lines are similar to the coast lines, and that some of the former 

 may be even closed curves. He showed that an untrue representation of tempera- 

 ture would be produced by introducing the artificial correction of 1° Fahrenheit 

 for every 300 feet above the sea level derived from observations in balloons ; and 

 he explained that it was owing to this untenable mode of altering the results of 

 observations of temperature that some recent maps deviate from those he had 

 originally produced. Among the absurd consequences of this artificial alteration 

 of observed results, he remarked that actual temperatures were in some instances 

 raised from 43° 6' to 47° 3', from 43° 3' to 47° V, from 42° 2' to 46° 6', and from 

 44° 4' to 48° 8'. A map of the distribution of plants would in these cases present 

 a semi-alpine or semi-arctic flora in contact with isothermal lines corresponding to 

 the flora of temperate regions. He maintained that the general law of distribu- 

 tion of temperature in islands surrounded by warm water currents, which he had 



* " Remarques a, propos d'une communication de M. Delaunay sur les resultats 

 fournis par l'Astronomie concernant l'epaisseur de la croute solide du globe." — 

 ' Comptes Rendus, Inst. France,' 1871, p. 250. 



f This Paper is published in extcnso in the 'Philosophical Magazine ' for Oct. 1878. 



