i882. 35 Trans. N. V. Ac. Set. 



quantities of these minerals in the powder under treatment being un- 

 equal. 



Dr. RiCKETTS replied that the investigations in which he had been 

 engaged were entirely of a practical nature, in which an accuracy 

 within one-fourth to one-half per cent, was aimed at, and for this the 

 use of a powerful magnifying glass was sufficient. The determina- 

 tion of the condition of the alumina and copper was not essential for 

 his purpose ; both probably existed as silicates. The method founded 

 on the solubilities of certain minerals had been found practically use- 

 ful, closely agreeing with the general run of analyses. The pure 

 zincite was considered the dark red mineral, colored by oxides of 

 manganese and iron, and its average amount in the ores of Franklin 

 had been determined and admitted as about six per cent. 



The Chairman remarked on the intricacy of the problem, which had 

 been the subject of this investigation, and ou the interesting and sug- 

 gestive solution which had been presented : the recognition of the 

 proportion of so large a number of minerals as occur .in this ore being 

 extraordinarily accurate. 



November 20, 1882. 

 Lecture Evening. 

 The President, Dr. J. S. Newberry, in the Chair. 

 The large Hall was filled to overflowing. 



The following letter from Prof. J. K. Rees, Director of the Ob- 

 servatory of Columbia College was read : 



(Abstract.) 



"I beg leave to call the attention of those members of the Academy pos- 

 sessing telescopes to the grand sunspot on the western portion of the 

 sun. Many of them have seen notices of this spot in the daily papers. 

 It deserves especial study in connection with the late displays of auro- 

 ras and the great electric storm, also as throwing some light on the con- 

 nection of comets and sunspots. This spot I have seen at noon, and 

 at four o'clock without a telescope, by protecting the eye with colored 

 glass. I saw it once without any protection to thej eye, by looking 

 through a narrow slit formed by my fingers. 



The great spot is really made up of several mutually encroaching 

 spots. Three nuclei are very well defined, and out into the darkest one 

 protrudes a penumbral finger. 



The disturbed region about this spot is about 80,000 miles square, 

 or covering 6,400,000,000 square miles. 



There are four other spots on the sun, three near the center'of^the 



