OF ARTS AND SCIENCES: APHIL 11, 1871. 311 



Remarks on this report were made by the President, Messrs. 

 Quincy, Lovering, Lyman, J. C. Gray, J. I. Bowditch, and 

 Shaler. 



A motion to suspend the publication of the second volume of 

 Count Rumford's Works was laid on the table, and the report 

 was referred back to the Rumford Committee. 



Professor Joseph Winlock exhibited some pictures of the 

 eclipse of 1870, and pointed out the resemblance between the 

 photographs of 1869 and of 1870. He also stated that in his 

 recording spectroscope it is not essential that the registering 

 point should be attached to the telescope, but to the part which 

 is moved for pointing on the lines of the spectrum. In Pro- 

 fessor Young's spectroscope, in which the prisms move, the 

 registering apparatus is attached to thena. 



Professor F. H. Storer presented the following paper on the 

 amount of carbonic acid in the air, by Mr. A. H. Pearson. 



The following paper contains an account of a large number of ex- 

 aminations of the air of various places for carbonic acid, made in the 

 chemical laboratory of the Massachusetts Institute of Technology, 

 during the spring of 1870, for the State Board of Health of Massa- 

 chusetts. 



They were made chiefly for the purpose of obtaining a general idea 

 of the amounts of carbonic acid in the air of school-houses and other 

 public buildings ; but there are also among them quite a number of 

 estimations of carbonic acid in the open air which may be of interest 

 when compared with similar examinations made in other places.* 



In these experiments the carbonic acid was determined by Petten- 

 kofer's method. This method consists in exposing a certain quantity 

 of standard baryta water to the action of a known volume of air, and 

 thus removing the carbonic acid as carbonate of barium. 



When the baryta water has been exposed to the air for a sufficient 

 length of time, the baryta remaining in solution is estimated with a« 

 standard solution of oxalic acid. 



The difference between the amounts of oxalic acid required to neu- 



* See Dr. R. Angus Smith, in the Scottish Meteorological Journal, January, 

 1870 ; also the Second Annual Report of the Massachusetts State Board of Health, 

 January, 1871. 



