50 BULLETIN OP THE 



sion 1890; declination at that time — 16*^.6; annual change in 

 ]870 — I'.O, and in 1880 — 0'.5. At this place the earliest observa- 

 tion dates from 1792.9 and the latest 1879.2. 



Results similar to the above are given for 52 stations; of these, 

 several are foreign, viz. ; Halifax, N. S. ; Quebec, Can., and 

 York Factory on the Hudson Bay; Havana, Cuba, Kingston, 

 Jamaica, Rio Janeiro, Vera Cruz, Mex., Mexico City, Panama, 

 New Granada and Acapulco, San Bias and Magdalena in Mex.; 

 Kailua, and Honolulu, Sandwich Islands, and Petropavlovsk, 

 Kamtchatka. 



Respecting errors of observations it is estimated that the ob- 

 servations made by Hudson in 1609 in the vicinity of our coast 

 and those of Champlain made about the same time may be sub- 

 ject to a probable error of ±: 4°. Observations in the 17th cen- 

 tury were frequently made on board ship in preference to terra 

 firma, as the land was supposed to attract the needle. The ob- 

 servations made by Vancouver on the western coast between 1792 

 and 1794 are subject to a probable error of only rfc 1°, and this 

 is about the present limit of uncertainty of observation taken at 

 sea with the azimuth compass and under favorable conditions, 

 whereas, with our present portable declinometers the observing 

 error is below 1', requiring a station to be occupied several days 

 in order to eliminate the daily regular and irregular fluctuations 

 of the magnet from the final resulting direction. 



The tables containing the decennial values of the magnetic 

 declination, as derived from the formulae, should not be extended 

 beyond the limit given to them (1885), though the expressions 

 may continue to represent the phenomenon, of the cause of which 

 no satisfactory explanation has ever been offered ; they may also 

 at any time fail ; in fact they need continued attention and adap- 

 tation for every new observation or development, and this must 

 continue so long as the process remains a tentative one, and we 

 are without an adequate theory to guide us. 



Remarks upon Mr. Schott's paper were made by Messrs. 

 Harkness, Alvord, and Elliott. 



Mr. J. S. Billings, Vice-President of the National Board of 

 Health, made a communication on 



the work of the national board of health, 



stating the various subjects to which its inquiries and investiga- 

 tions had been directed and the progress made. 



Remarks were made by Messrs. Mason, Osboene, Antisell, 

 Newoomb, Woodward, and Toner, and the discussion extend- 

 ing to the disinfection of ships. 



