On the Stihjecl of Navigation. 51 1 



been ufed, the natural conclufion would have been, that the 

 Ore was a mixture, or at mod a combination, of thefe two 

 fubfiances; tor fuch did it appear to he l)v ihc tcliimony of 

 the other acids. The truth is, we are but little acquainied 

 with the exaft ftate in whicli fubfiances exitt in many na- 

 tural combinations. However, in the mineral kingdom, fuch 

 fall icious conckifions are lefs frequently to be dreaded than 

 in the vegetable and animal kingdoms. But, in every re- 

 fearch, it is important to leave as little room for them as pof- 

 fiblc ; and he who would indicate a fure and confiant method 

 of afcertaining whether, in manv cafi s, what we deem a com- 

 ponent part, is not, in faft, a produ^-l; of the operation, would 

 render to fcience a fervice, the real value of which is, per- 

 haps, not now entirely forefeen. 



Llir. Commiinlcatiojis on the SiihjcB of Na-z'igutioTi, from 

 John Cookk, Efq\ M.R.I. A. 



■Y SIR, Duiiiin, April 2:;, i?02. 



X REQUEST permiffion to communicate to the public, 

 through vour Magazine, the inclofed attempts to advance 

 the art of navigation; they confill of methods ot uieafuring 

 diftancc at fea, and of difcovering currents, with the plan of a 

 new fea chart. Mv ol)ii.'d in publidiing them is to offer them 

 to the confideration of others who are more capable of de- 

 tecting their imperfe(!^ions and of fugiicftiug remedies than 

 myfelif, for which I Hiall be thankful ; but, as 1 intend to 

 make experiments, and to follow up tlvjfe inventions, I do 

 not wi(h to have it underllood that I relin<|ui(li my exclufive? 

 right to them by this (iep, or that any perton may make ufe 

 ef them without my confent. I am, Sir, 



Vour moll obedient fervant, 

 To Mr. Tilkch. John Cookr. 



THE di fiance through which a fliip fails is the product of 

 the time and velo'ity of its progrefs : the time is eafily af- 

 certained by well-known methods, and the log-line exhibits 

 the decree Of motion during tlie cx|)eriment with tolerable 

 certainty : but, fmce the motion is perpetually v-arying, this 

 n)(lhod would re(juire an uninterniptcd lucrellioii of experi- 

 inenls to afford an accurate meafure ; therefore it is a defuie- 

 raiiun in naviiiation to obtain lomc eafy method of regificr- 

 inir the fevirardian-rcs of velocity »\hich fake place in fail- 

 ing, Willi the interval-; of lime bclwcen each ; wliicli objci'-ts, 

 I' 4 wiih 



