The Rev. J. B. Harbord on the Conic Theory of Heat. 185 



same element may be present in opposite states : such consti- 

 tuents would have their places accordingly,, though with subor- 

 dinate groupings, according to special affinities. 



In order not to be misunderstood, I here state formally, what 

 has been more than once implied in the foregoing, that while, 

 according to the principle advanced, tetragonal and hexagonal 

 forms depend on the numbers 4 and 3, as explained, the pre- 

 sence of these numbers by no means necessitates the occurrence 

 of these forms. Multitudes of examples illustrate this : the di- 

 morphism of TiO 2 is one. I would also remark that I express 

 no opinion as to whether the molecule of a compound consists of 

 the positive and negative atoms simply juxtaposed, or whether 

 these so-called atoms are composed of particles, and there is a 

 different disposition in the molecule, — and assert only that, what- 

 ever the fact on this point, there is tetragonal symmetry in the 

 constitution of the molecule in the tetragonal system, and hexa- 

 gonal in the hexagonal system. 



I leave the subject here, without discussing at present the 

 methods by which orthorhombic and clinohedral forms are pro- 

 duced, — only observing that orthorhombic and monoclinic forms 

 occur under all numbers of atoms of the negative element, from 

 1 (or 2, as in sulphur) upward, and therefore, although poly- 

 merism may turn the 2 of sulphur (and, so, other numbers) into 

 various multiples of the same, yet that the production of these 

 forms does not depend simply on numbers. 



XXIII. The Conic Theory of Heat considered in connexion with 

 General Sensation and the three senses of Touch, Taste, and 

 Smell, By the Rev. J. B. Harbord, M.A. 



HUYGHENS, in his advocacy of the undulatory theory of 

 light, drew attention to the manner in which our various 

 senses are affected by external objects, near and distant ones, 

 pointing out as a probable conclusion that light is propagated in 

 a similar manner as sound — by waves. Such an argument may 

 not appear to be worth much now that the truth of the theory 

 is established, but doubtless it helped at the time to mature and 

 confirm a controverted hypothesis. While philosophers are still 

 unagreed as to the exact nature of the motion of heat, it may not 

 be altogether useless to direct attention to those of our faculties 

 which take cognizance of heat and the effects of heat in the 

 metamorphosis of matter. An examination of these will, I think, 

 furnish considerable presumption in favour of such a theory as 

 that of Rankine, which makes the gross molecules of substances 

 revol/e about undulating nuclei of aether. 



* Communicated by the Author. 



Phil. Mag. S. 4. Vol. 34 No. 229. Sept. 1857. O 



