Roi/al Society. 129 



Chapter 2. Problems. — To find the Perspective of Points on the 

 Ground Plane j — Perspective of a line oblique to Plane of Picture j — 

 Of a Line perpendicular to same ; — Parallel ; — Perspective of Trian- 

 gles ; — Of Parallelograms ; — Perspective of Divisions of Lines, equal 

 or proportional ; — Perspective of Curves ; — Of Circles ; — Curvili- 

 near Lines generally ; — Volutes and Spirals ; — Inscriptions ; — For 

 finding Perspectives without inversion of original ; — Of the general 

 bearings of Squares and Parallelograms, with their Diagonals. 



Chapters. Of Solids. — Right-angled Quadrangular Structures ; 

 — Their Faces and Sides with symmetrical Breaks and Divisions j — 

 Of Planes oblique to Horizon Planes ; — Elevations on Circular Planes 

 (as Columns, &c.) ; — Paradoxical appearance of equal Circles and 

 Cylinders ; those at the sides larger than the central ; — In Perspec- 

 tive, diameter not the longest Line ; — Sections of Solids, horizontal j 

 — Vertical ; — Relative Magnitudes and Heights of Objects. 



Chapter 4. Summary, and additional Remarks j — Various methods 

 of dividing Surfaces J by Diagonals j — By proportional Triangle; — 

 Scale for Division extended beyond the Picture; — Contrivance for 

 Ruling or Proving a multitude of Lines vanishing together; — Shorter 

 Method of putting Circles in Perspective; — Geometrical Plan for 

 Circles of all sizes; — Of Mechanical Instruments; — Camera-Lu- 

 cida ; — Divided Frame for choosing a view; — Further consideration of 

 Horizon-line, — Point of distance, — Field of Vision, — Necessity of 

 placing the Zero Point in centre of Picture, — Perspective of very 

 high Vertical Lines and Spaces, — Difficulty of Down-hill Views, and 

 of Levels much below the Eye, — postponed. Conclusion. 



XXL Proceeditigs of Learned Societies. 



ROYAL SOCIETY*. 



June 5, "/^N the laws of the deviation of magnetized needles 



1 828, yJ towards iron," by S. H. Christie, Esq. M.A. F.R.S. &c. 



The author had pointed out, several years ago, the law of deviation 

 of a magnetized needle, (either freely suspended, or constrained to 

 move in any particular plane,) from its natural position, by the influ- 

 ence of masses of iron in its vicinity. This law was founded on (he 

 hypothesis, that the iron attracted both the poles of the needle ; the 

 position of which, resulting from this action, might be determined 

 by that of an imaginary minute magnetic needle, freely suspended by 

 its centre of gravity, reduced to the plane of revolution. The author 

 had considered this law as fully established, from its accordance with 

 experiment : but Mr. Barlow, in a paper which was published in the 

 last volume of the Philosophical Transactions, denies that such an 

 accordance exists, and infers from the results of some experiments 

 which he made on horizontal needles having their magnetism un- 

 equally distributed in their two branches, that the theory on which the 

 preceding law is founded is fallacious. In opposition to the views of 



* The portion of the proceedings of the Royal Society iiere given, con- 

 sists of abstracts of tiic papers read at the meetings at the end of the session 

 1827-8. 



New Series, Vol. 5. No. 26. Feb. 1829. S Mr. 



