304 VARIATION OF THE COMPASS. 



It is much to I Cannot conclude ihis Paper without expressing my regrel:, 

 he regretted tJ^at so little avail should have been made of the numerous 

 tions of varia- opportunities which have been afforded to trarellors and 

 tions have not others, in the last century, for making accurate observations, 

 njade'^ *^"*^'^ ^^''^'^ proper instruments, at land, on the variation in different 

 parts of the world. Such observations would probably have 

 afibrded some curious and useful facts, which would have ma- 

 terially assisted in forming a theory much more certain than 

 what we at present possess ; the present received opinion of 

 the cause of the diurnal alteration of variation would be con- 

 firmed or invalidated; its quantity of effect in different places, 

 a most desirable acquisition, would be ascertained ; and we 

 should be put in possession of more valuable and correct 

 information on the variation than can be derived from obser- 

 vations made with the common azimuth compass, even at 

 land, owing to its imperfect construction. The variation thus 

 accurately obtained at any one period, compared with the 

 variation correctly ascertained at a subsequent period, would 

 give a rate of alteration of the variation which could be relied 



Oborvalions ®"* 



and researches The celebrated Halley thought the variation of so much 

 CI Halley, importance, that he made t\yo voyages for the purpose of 

 making observations on the variation, to confirm his theory 

 advanced in 1613, and soon after he published his variation 

 chart* Since his time no better theory than he left has been 

 obtained, although it must be confessed that many observations 

 have been made at sea by voyagefs; but these observations, 

 made generally to answer the purpose of the observer at the 

 time only, are therefore seldom preserved ; for, unless made 

 by authority, which rarely happens, they do not often meet 

 the public eye; and it must be from observations made with 

 care, and with good instruments, carefully registered, and 

 properly arranged, that any real advantage can be derived. 

 It is hoped therefore, that, in future, attention to this subject 

 will not be thought beneath those who may have it in their 

 power essentially to promote an undertaking so interesting to 

 the philosopher, and so valuable and useful to the maritime 

 world. 



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