430 Cambridge Philosophical Society. 
fluids; for the former a particular function of the forces was always 
negative—tor the latter always positzve ; which remarkable circum- 
stance the author thinks will lead to the most important conse- 
quences in the theory of molecular actions, 
The Rev. Mr. Whewell madesome remarks on the present state of 
our knowledge of the tides. He stated that recent researches have 
completely changed the position of this subject ; observation is now 
in advance of theory, as, a little while ago, theory was in advance 
of observation. It has been shown that the inequalities depending 
on the moon’s hour of transit, declination, and parallax follow with 
great exactness the laws resulting from the hypothesis of a spheroid 
of equilibrium, slightly modified. In addition to this, it has recently 
been discovered that the diurnal inequality of the tides agrees in 
general circumstances with the equilibrium hypothesis, and that 
there is a solar inequality also agreeing with the same hypothesis, 
The observer may now, therefore, call upon the mathematician to 
investigate the result of some theory agreeing more nearly with the 
state of the case than those of Bernoulii and Laplace, and thus to 
bring the calculation into accordance with the observed quantities. 
It was remarked further, that this must be solved as a problem of 
hydrodynamics, not of hydrostatics; but that it does not appear 
likely that a satisfactory solution will be obtained, except we take 
into account the retarding forces, as well as the attractive forces 
and the condition of perfect fluidity. ‘This being almost the only 
mechanical problem yet unsolved, which is requisite for the com- 
pletion of the theory of universal gravitation, was put forward as a 
subject well worthy the attention of mathematicians. 
March 7.—Mr. Whewell gave an account of the recent discoveries 
made by Prof. Forbes, and other philosophers, with respect to the pola- 
rization of heat. Ele stated that Prof. Forbes had recently obtained 
an additional confirmation of this discovery, by finding that heat, by 
two internal reflexions in a rhomb of rock-salt, resembling Fresnel’s 
rhomb, becomes circularly polarized under the same circumstances 
as light. It was also mentioned that Biot and Melloni have very 
recently ascertained that heat acquires circular polarization by trans- 
mission along the axis of a crystal of quartz.* 
The Rev. Mr. Willis then explained his views respecting the com- 
position of the entablature of Grecian buildings. He observed that 
this feature in the architecture of Egypt consisted of two members, 
arising from the mode there adopted of roofing a building with beams 
of stone, resting on the pillars, and supporting transverse slabs. The 
upper member being resolved into two, the three divisions of archi- 
trave, frieze, and cornice were produced; and the portion of the 
mass which belongs to each of these members may be determined 
by observing in what manner they are managed when the entabla- 
ture is resolved into parts by cross-trabeation. It appears in this 
way (and also by the principles which, Vitruvius implies in giving 
his rules) that each member consists of a vertical face capped by 
* See the report of proceedings of the Royal Society of Edinburgh, in 
the preceding page. 
