380 Royal Society : — ■ 



A valuable service would be rendered to this very important 

 branch of hydrography, if, under the authority of the new depart- 

 ment of the Board of Trade, variation-charts for the North and 

 South Atlantic Oceans, for the North and South Pacific Oceans, for 

 the Indian Ocean, and for any other localities in which the require- 

 ments of navigation might call for them, were published at stated 

 mtervaJs, corrected for the secular change that had taken place 

 since the preceding publication. Materials would be furnished for 

 this purpose by the observations which are now intended to be 

 made, supposing them to be collected and suitably arranged with 

 proper references to date and to geographical position, and to the 

 original reports in which the results and the data on which they 

 were founded were communicated. By means of these observations 

 the tables of approximate correction for secular change might also 

 be altered from time to time as occasion should require, since the 

 rate of secular change itself is not constant. 



All observed variations, communicated or employed as data upon 

 which variation-charts may be either constructed or corrected, should 

 be accompanied by other observational data (the nature of which 

 ought now to be well understood), for correcting the observed varia- 

 tion for the error of the compass occasioned by the ship's iron. It 

 is also stronglj' recommended that no observations be received as data 

 for the formation or correction of variation-charts, but such as are ac- 

 companied by a detailed statement of the principal elements both of 

 observation and of calculation. Proper forms should be supplied for 

 this purpose ; or, what is still better, books of blank forms may be 

 supplied, in which the observations themselves may be entered, and 

 the calculation performed by which the results are obtained. Such 

 books of blank forms would be found extremely useful both for the 

 variation of the needle, and for the chronometrical longitude (as 

 well as for lunar observations, if the practice of lunar observations 

 be not, as there is too much reason to fear it is, almost wholly dis- 

 continued). By preparing and issuing books of blank forms suit- 

 able for these purposes, and by requesting their return in accompa- 

 niment with the other reports to be transmitted to the Board of 

 Trade at the conclusion of a voyage, the groundwork would be laid 

 for the attainment of greatly improved habits of accuracy in prac- 

 tical navigation in the British mercantile marine. 



The President and Council are aware that they have not exhausted 

 the subject of this reply in what they have thus directed me to ad- 

 dress to you ; but they think that perhaps they have noticed as 

 many points as may be desirable for present attention ; and they 

 desire me to add, that they will be at all times ready to resume the 

 consideration if required, and to supply any further suggestions 

 which may appear likely to be useful. 



I have the honour to be. Sir, 



Your obedient Servant, 

 W. SHARPEY, 



Sec. R.S. 



The Secretary of the Lords of the Com- 

 mittee of Privy Council for Trade. 



