300 Variation and Dip of the Magnetic Needle. 



gable observer, that, with clock-Hke regularity, at the expiration 

 of every five years, returns to measure the magnetic variation ; 

 and how dees his zeal reprove the sluggishness of the scientific 

 institutions in our country, at many of which the variation of the 

 needle has not been even once observed? (5.) The table does 

 not purport to be a table of observations, but to be " agreeable to 

 the actual observations distinguished by Obs." The numbers 

 marked Obs. were then observed, and the others were computed 

 from them, so that six observations were the foundation of the 

 whole table. The matter appears to me so plain, that it seems 

 useless to argue the question further. The table which is given 

 in volume sixteenth of this Journal, has copied the errors of 

 Ames's almanac, and thus, by introducing a httle irregularity into 

 the numbers, has given them more the air of actual observations. 

 The table is still further disguised, by omitting the Obs. which 

 marks certain numbers in the original table. If now I have suc- 

 ceeded in showing that this " interesting document," as Mr. De 

 Witt terms it, contains but six actual observations, I shall consider 

 that I have effected no small object ; for it certainly is a fact not 

 very creditable to American science, that a table which Prof. Win- 

 throp, nearly three quarters of a century ago, computed for his 

 own amusement, should now be referred to as copiposed of genu- 

 ine observations. I have taken the more pains to expose this 

 imposition, (for imposition I think it may be called, although a 

 perfectly honest one on the part of Prof. Winthrop,) because it is 

 necessary to be particularly on our guard against confounding cal- 

 cfiilations with observations, and because in the progress of my 

 investigations, I have met with other tables similar to the prece- 

 ding one of Prof. Winthrop. 



I have now mentioned all the new magnetic observations which 

 I have been able to collect, and have also stated where other pub- 

 hshed observations are recorded. The results of all these are 

 embraced in the following general table : 



