294 OBSERVATORY. [CHAP. XXXVI. 



slant difference, first pointed out by Mr. J. F. Ste 

 phens, in the markings of the beautifully coloured 

 anterior wing. On an accumulation of facts of this 

 kind must depend ultimately the answer to that 

 difficult question, What is the difference between a 

 species and a permanent variety ? How far can 

 climate, food, heat, light, and other causes give rise 

 to fixed and constant modifications in individuals 

 descended from one parent stock ? 



We ascended the hill, on which a new observatory 

 has been built by subscription since we were last 

 here, and where there is an equatorial telescope 

 seventeen feet twelve inches in diameter. Dr. 

 Mitchell, the astronomer, proposes to explore a part 

 of the heavens more to the south than that which falls 

 within the range of any active European observatory. 

 From this hill we had a fine view of the winding 

 valley of the Ohio, and the city on its banks, with 

 nearly 100,000 inhabitants, the flat terraces of loam 

 and gravel bordering the river, and the wharf with 

 its fleet of steamers. On the opposite side of the 

 Ohio is the town of Covington in Kentucky, the 

 streets of which are made so to correspond with 

 those of Cincinnati, that they appear as if they were 

 parts of the same city, and a bridge over the river 

 is in contemplation. 



The height of the hills above the river is about 

 400 feet. The trees are still in great part leafless, 

 but our eyes were refreshed with the green sward 

 adorning the sloping banks, such as we had not seen 

 during our winter tour in the Southern States. 



The German settlers have greatly extended the 



