PHILOSOPHICAL SOCIETY OF WASHINGTON. 8t 



only be read as zero. It is evident, therefore, that 0.35 of the 

 zeros froai chronograpli A should be read as ones. 



As the length of the interval is reduced by using a smaller 

 cylinder, the adjustment of the length of the clock-mark to ^l of 

 a second becomes more difficult, and, accordingly, we find not 

 only the ones, but the twos and nines affected in the work from 

 chronograph B. 



Representing the number of zeros in a series of observations 

 of the same object by N, and the number of complete observa- 

 tions over nine threads by 7i, the probable correction to be applied 

 to the mean result of observations taken from chronograph A 



n 1 ^X 0.35 



would be , 



dn 



and from chronograph B ^_ (0-34-f 2x0.11 - 0^ _ ^X 0.52 



The adjustment of the clock-mark to less than -^^ of a second 

 for chronograph B requires a strong and constant battery power, 

 which can only be secured by such assiduous watching that it 

 becomes nearly impracticable in neai'ly all routine astronomical 

 work. This difficulty can be reduced one-half by allowing the 

 clock to mark only ouce in two seconds; but the only complete 

 solution of the problem seems to be to increase the length of the 

 interval. 



Mr. Joseph Henry, in the absence of Mr. C. S. Peirce, gave 

 the third of his lectures 



ON ATMOSPHERIC ELECTRICITY. 



4Yth Meeting. May 10, 1813. 



Vice-President J. E. Hilgard in the Chair. 



The Chair announced that in respect to the memory of the late 

 Chief Justice, Salmon P. Chase, the general committee had de- 

 termined that this meeting of the Society should be adjourned for 

 one week. Dr. Peter Parker then presented, with some appro- 

 priate remarks, the following Resolutions, which were adopted: — 



Whereas, since the last meeting of the Philosophical Society 

 of Washington, Salmon Portland Chase, Chief Justice of the 

 United States, an esteemed and honored member of this Society, 

 has departed this life full of years and full of honors, no more to 

 meet his associates here : 



