SEA LOG AND SOUNDING MACHINE. ^49 



the cunents ia various parts of the ocean, which has hiihertoknowlcdge or 



been very imperfectly attained; as it was not possible to '^"'^'^^"^^' 



know, with any certainty, whether the wide difference found 



between the real distance, and that given by the common 



iog^, was caused by the known imperfections of that method 



of reckoning, or by the operation of currents. 



Dr. Maskelyne, in the same work just quoted, further Remarks oft 



observes: " There is another arg-iiment which adds much *^"* ^V ^i^- 

 , , „ . ° , , r> Maskelyni* 



** strength to the loregonig ones, and greatly eniorces a 



" uniform and correct length of the loghae, on board ajl 



*' ships; that in many parts of the ocean, especially be- 



*' tween the tropics, and near most head-lands, there are 



*' considerable cunents, which must introduce a fresh er- 



** rourinto the reckoning; and if this errour should happen 



*' to combine with that already produced by a wrong length 



** of the logline, as it may as well as not, it is not easy to 



** say how far the total errour of the reckoning might go, 



" or to what inconveniencies or dangers the ship might be 



" exposed on that account. But if the just and proper 



*' length of the logline were used on board of all ships, 



•' they would be then liable only to the errours of the eta- 



** rents themselves; and even these, as far as they are con- 



** stant and regular, might be found out and ascertained, 



** from the journals of several ships, which would then agree 



'■' much nearer with one another." And Smeaton observes, and Mr. 5'i«c*« 



** that it is for want of a means of measuring the way of a ''^"* 



" ship through the water, (and this compared with other 



" check observations,) that the drift and velocities of the 



'* principal currents have not already been determined.'* 



Butadmittingtliecommon logline and glass were perfect- 

 ly uniform in each ship of a fleet, yet the result would still 

 be too erroneous to expect this very desirable knowledge of 

 the currents to be derived from a comparison of the several 

 journals. Massey's patent log holds out, however, more 

 than a probability of effecting this important end. It ap- p^^'ckoninR to 

 pears by a letter from Captain Whittle, of the Lord Nelson, Ne^rfoull<■ilJnd 

 that he found the distance run from the island of Ila, to St. ^,*1'|^^ n'tes-^ 

 John's harbour, Newfoundland, by Massey's log, to agree 

 with the known latitudes and longitudes of b«th places, 

 within *ight miles. Now had he sailed in company with se- 

 veral 



