CHAIRMAN'S ANNUAL REPORT. 215 



of the results possible from its use. Professor Cooley 

 also called attention to the most serious difficulty in 

 manipulating this instrument— the optical difficulty in 

 the reading of the scale in the cross-lights of an or- 

 dinary room. He described a simple contrivance, by 

 means of which he had succeeded in entirely over- 

 coming this disadvantage. 



On February 11 a paper was read by the chairman on 

 "The Peculiar Structure of Clark's Clay-beds, near 

 Newburgh, N. Y." 



February 25 was filled by the closing paper, by Dr. 

 Warring, on gyroscopic movements, entitled, " Various 

 Results and Final Studies ; Precession of the Equinoxes ; 

 Frisi's Law, and Other Topics." This paper, like the 

 preceding ones, was ingeniously illustrated, and fur- 

 nished much material for thought on the mysteries of 

 gyroscopic motions. 



March 11 a paper was presented, by Prof. Maria 

 Mitchell, on "Recent Celestial Phenomena." On ac- 

 count of the illness of Professor Mitchell, the paper was 

 read by her assistant, Miss Mary Whitney. 



On the same evening, Miss Mary Whitney presented 

 a paper on " Sun Spots," founded to a considerable ex- 

 tent on her x^ersonal observations. 



On March 25 Dr. De Garmo, having been prevented by 

 illness from reading an expected paper, the evening was 

 occupied pleasantly by the consideration of various 

 miscellaneous items. Mr. C. IS". Arnold took this oc- 

 casion to exhibit to the section, accompanied by ex- 

 planations, a fine set of ferns of this vicinity and other 

 parts of the country, mostly collected and carefully 

 mounted by himself, which collection he also presented 

 to the Museum of the Institute. 



The last meeting for scientific work on April 8 was de- 

 voted to the microscope and to miscellaneous communi- 

 cations. Several microscopes were brought to the hall 



199 



