362 On the Circle. 



of water and caiboiiic acid gas, the theory of definite prqior- 

 tioiis is beautifully preserved. 



I feel now anxious to detail to vou an experiment which may 

 serve to benefit the cause of humanity — a cause to which I pro- 

 fess nivself warmly attached. I came from the North on the 

 top of the Glasgow mail, and had " to bide the pelting of the 

 pitiless storm," the inside scats being pre-engaged from Carlisle. 

 On the road we encountered a fierce snovv-storm. The coach- 

 man and myself were nearly blinded by themiintermitting flalics, 

 and the poor animals the horses were as painfully situated, and 

 expressed as much. At the immediately succeeding stiige I pro- 

 cured a pfece of black crape, and attached it to the lining of the 

 hat, so that it huiio; vertically before the eye. This I found 

 not only to prevent the snow from injuring the visual organ, by 

 warding it off; but at the same time, by cutting off the adven- 

 titious rays, I was enabled to obtain a more Jislmct and better 

 defined view than I else should have had. This provision also 

 prevented the eve from being dazzled by tlie reflection of light 

 from the surface of snow, f ^rape being an uneven surface, black 

 lace work with line open meshes might serve better. 



By mariners at sea, &c. this may be held to merit atten- 

 tion. 



I am with high respect, sir. 



Your obedient servant, 

 Surry Institution, Nov. 15, 1816. J. MuRRaY. 



P. S. I was much gratified to find the miners in a colliery near 

 Ayr, conducting their operations solely by the light exhibiled hy 

 the fire-damp — formerly so terrible an engine of destruction. 



J. M. 



LXXIV. On the Circle. 

 To Mr. Tilloch. 



Sir, — zx Correspondent of Dr. Thomson's (Annals of Phi- 

 losophy, Junel816, p. 4f)S), has attempted to demonstrate that 

 no part of a circle is a straight line. It may be supposed that 

 this proposition is so evidently correct, as to render demonstni- 

 tion unnecessary. But however absurd the idea that curves are 

 composed of small right-lines may apj)ear, it is, either directly 

 or indirectly, the foundation of most of the theorems relating 

 to curves. A perfect circle can only be imaginary ; there is jio 

 scich thing in nature, and art is incapable of producing oive. 



The 



