OF DERWENT LAKE. 23 



where its summit first appears above the rising 

 ground near Sunderland, I have found about 

 21 feet perpendicular. It generally seems highest 

 in the morning, and once in particular, after a 

 clear night, it appeared much higher than at 

 any other time of my observation. The distance 

 from Castlehead to CrifFell, is about thirty miles, 

 and the intercepting ridge of land about one- 

 third of the distance from the former place.* 



An appearance which I first noticed in 1812, 

 when we were at Wasdale Head, I have had 

 frequent opportunities of observing since; but 

 I think, that till lately, I formed an erroneous 

 conclusion as to the cause. It happens on a 

 clear dewy morning, when walking on ground 

 sloping to the west, so that the shadow of my 

 head falls at a considerable distance ; then it 

 appears surrounded by a kind of liuninous circle, 

 for which the only cause that occurred to me, 

 was, that a warmer and more vapoury atmos- 

 phere might surround my head, so as to refract 

 the sun's rays in a peculiar manner. But one 

 morning, when upon Castlehead, the shadow 



* The reader will perceive these remarks relate to the 

 variable refractive power of the atmosphere at low altitudes. 

 Criffel is a Scotch mountain seen from Keswick, over Solway 

 Firth. Its summit is about 1830 feet above the level of the sea. — 



J.D. 



