Variation and Dip of the Magnetic Needle. 299 



The table which is given in Ames's Almanac for 1771, is ex- 

 actly like the preceding, with six exceptions, viz. the variations 

 for Boston are given 9° 45' for 9° 46' ; 8° 5T for 8° 51' ; 6° 45' 

 for 6° 46' ; and 5° 35' for 5° 36'. In the column for Falmouth 

 is given 10° 12' for 10° 17', and in the column for Penobscot 8° 

 32' for 8° 35'. I have no doubt that these were typographical 

 errors in the almanac, and that the sheet in the possession of Mr. 

 Adam Winthrop, which was doubtless printed under the eye of 

 Prof. Winthrop, is the correct copy. It is evident that the prece- 

 ding table was entirely computed, with the exception of those 

 numbers marked Obs. For (1.) the table was published before 

 1771. One quarter of the numbers were then certainly compu- 

 ted. (2.) The variations for Falmouth are constantly 45' greater 

 than those for Boston, and those for Penobscot 8' greater than 

 those for Falmouth. To one who has ever made magnetic ob- 

 servations, this will amount to an absolute demonstration that 

 those numbers were never observed. (3.) The observations from 

 1700 to 1800, with the exception of those marked Ohs., all occur 

 at intervals of five years, and the change of declination for this 

 period is constantly 14' or 15'. The observations of 1742 and 

 1763, showing a change of one degree in 21 years, or somewhat 

 more than 14' in five years, doubtless furnished the data for the 

 table. (4.) Penobscot and Falmouth, during the first years con- 

 tained in the table, were small settlements. Penobscot was little 

 more than a military post, and Falmouth was devastated by the 

 Indians in 1692, and the town entirely broken up. The inhabit- 

 ants did not return until about 1708. Who then is this indefati- 



