328 



with regard to light, is slightly reflective and imperfectly transpa- 

 rent ; it decreases in size, but increases in density and light reflec- 

 tive power in approaching the perihelion, and the reverse when re- 

 ceding from it ; and this occurs in a degree proportioned to the ex- 

 centricity of the orbits of the comets. 



llth, The axis of the tail of a comet is straight at the perihelion, 

 but at any point between this and the aphelion, is curved; and is 

 concave towards the latter, the i-adius of curvature being inversely 

 as the excentricity of the orbit. 



12th, The molecules composing the envelope of a comet are only 

 held together by their mutual gravitation, each constituting almost a 

 separate independent projectile, and describing its own parabola about 

 the sun. 



3. Abstract of Professor Kelland's Exposition of the Views 

 of D. E,. Hay, Esq., on Symmetric Proportion. 



The fundamental hypothesis of the author was stated to be this : — 

 That the eye is capable of appreciating the exact subdivision of 

 spaces, just as the ear is capable of appreciating the exact subdivi- 

 sions of intervals of time ; so that the division of space into an exact 

 number of equal parts will affect the eye agreeably in the same way 

 that the division of the time of vibration in music, into an exact num- 

 ber of equal parts, agreeably affects the ear. But the question now 

 arises. What spaces does tlie eye most x'eadily divide 1 It was stated 

 that the author supposes those spaces to be angles, not lines ; believ- 

 ing that the eye is more affected by direction than by distance. The 

 basis of his theoi*y, accordingly, is, that bodies ai'e agreeable to the 

 eye, so far as symmetry is concerned, whenever the principal angles 

 are exact submultiples of some common fundamental angle. Accord- 

 ing to this theory we should expect to find, that spaces, in which the 

 prominent lines are horizontal and vertical lines, will be agreeable to 

 the eye, when all the principal parallelograms fulfil the condition 

 that the diagonals make with the sides, angles which are exact sub- 

 multiples of one or of a few right angles. This application of the theory 

 was exemplified by a sketch of the new Corn Exchange erected in 

 the Grassmarket by David Cousin Esq., whose beautiful design was 

 shewn to have been constructed with a special reference to the fulfil- 

 ment of this condition. 



The author was stated to proceed to apply his theory to the con- 



