295 



The length of this comet was at first 120°, decreasing very 

 rapidly at the rate of about 25° daily. 



A third comet, not, however, a new one, is now visible. 

 Mr. H. gave an account of the discovery of this comet, the 

 discussion and determination of its orbit (three and a half 

 years) by Encke, and most interesting of all the important 

 part this comet had played in the determination of the 

 mass of Mercury, and the existence of an etherial medium 

 which had retarded its motion about one hour in each revo- 

 lution. 



At the close of Prof. Hough's paper, an interesting 

 discussion followed in regard to personal equations, in 

 different observers, and the methods used for determin- 

 ing it. 



After which, it was announced that at the next meeting 

 Prof. Hall would present a communication on the Geology 

 and Geological Survey of Wisconsin, illustrated by maps 

 and charts. 



The Institute then adjourned for three weeks. 



January 7, 1862. 



The president, Mr. Pruyn, presided. 

 The following donations were announced : 

 Memoirs of American Academy of Arts and Sciences, 

 Yol. VIIL, from the Society. 



The Plains of Long Island, from Col. Johnson. 

 The Potato, its Diseases, from Col. Johnson. 



On motion of Mr. Murray, it was resolved that at the 

 next regular meeting, the Institute proceed to the annual 

 election of officers. 



Prof. Hall then presented his communication on the 

 Geology and Geological Surveys of Wisconsin. 



After some general remarks on the geology of Wisconsin, 

 he proceeded to speak more particularly of the lead region. 

 All the lead deposits of any extent are found in what is 

 termed Galena limestone, a magnesian limestone. In this 



