OF ARTS AND SCIENCES. 197 



Fowr Iiuudred and sixty-fourth meeting. 



April 12, 1859. — Monthly Meeting. 



The Academy met at the house of Dr. J. M. Warren. 



The President in the chair. 



Professor Peirce reported favorably on Mr. SafFord's paper, 

 which had been reftrred to him at the last monthly meet- 

 ing, recommending its reference to the Committee of Pub- 

 lication. The report was accepted, and the recommendation 

 adopted. 



Dr. Warren exhibited a specimen of Cheironcctes, and ex- 

 plained some of its peculiarities of structure and habits. 



Dr. Warren also exhibited a suite of specimens of crania 

 and casts of crania of the different species of Ourang, includ- 

 ing the great Troglodytes Gorilla of Western Africa, together 

 with stuffed specimens of the Chimpanzee : he pointed out 

 the characteristic features of the different species, and exhib- 

 ited lithographic illustrations of the gigantic Gorilla now in 

 Paris. He also exhibited specimens illustrating the progress 

 of the new art of photolithography. 



Professor Peirce gave the following abstract of a memoir 

 on the personal peculiarities of astronomical observers. 



" The first portion of this memoir considered the changes which 

 occur in the personal equations of observers. The materials for this 

 inquiry were derived from that vast reservoir of astronomical investi- 

 gation, the ' Greenwich Observations,' since it has been under the able 

 administration of Professor Airy. The mode of determining the per- 

 sonal equation adopted at this observatory, from the regular obser- 

 vations, and not from especial observations instituted for this purpose, 

 is the only one which is safe and trustworthy. From these observa- 

 tions, it appears that observers differ greatly fi-om each other in the 

 continuity and regularity of their habits. There are those who retain 

 for many years, as nearly as it can be ascertained, an invai'iable per- 

 sonal equation. Others change uniformly and regularly. Others seem 

 to vary by a uniformly increasing or decreasing rate of change ; while 

 others, on the contrary, are subject to sudden and abrupt variations, 



