298 Variation and Dip of the Mag?ieiic Needle. 



In the preceding enumeration, I have not included a table of 

 magnetic variations which is given in Vol. xvi, page 63, of this 

 Journal. This table professes to give the variation of the needle 

 at intervals generally of five years, from 1673 to 1800, for Bos- 

 ton, Falmouth, and Penobscot. I have rejected the table, be- 

 cause I am satisfied it is a calculated table. This assertion will 

 sound strange to some, for I have more than once been referred to 

 it by men of science, as a repository of exceedingly valuable ob- 

 servations, and they seem never to have suspected that the obser- 

 vations were not genuine. But there is no room for the shadow 

 of a doubt, that those numbers were mostly calculated. The evi- 

 dence is as follows : The table is a very old one, being found in 

 the Almanac for 1771, by Nathaniel Ames. A copy of this al- 

 manac is in possession of Mr. William Lyon, of New Haven. 

 There is also in the possession of Mr. Adam Winthrop, of Lou- 

 isiana, grandson of Prof. Winthrop of Harvard University, a 

 small printed sheet, in the form of a handbill, containing the 

 same table. It is without date, but bears marks of age, and was 

 found among the papers of Prof. Winthrop. It is my opinion 

 that this is the original from which the table in the almanac was 

 copied, and as it is a document to which circumstances have given 

 considerable consequence, I have here transcribed it verbatim. 

 " A table, exhibiting the variation of the compass in Boston and 

 the parts adjacent, from the earliest accounts of it to the end of 

 the 18th century ; agreeable to the actual Observations distin- 

 guished by Obs. By John Winthrop, Esq., Hollisian Professor of 

 Mathematics at Harvard College, in Cambridge, in New England. 



