'69 J Farialion of the Magnetic Needle. — Marine Thermometer. 



by Mr. Allaire, and is supposed to be the most powerful and most 

 exact piece of workmanship ever turned out in America j and her 

 boiler is said to l)e the largest ever known to have been made in 

 that or any other country- — yJmerican Paper. 



A royal brig, called Le Vbyageur, was lately fitted out at 

 I/Orient for a vovage to Senegal, as a steam-packet, the first of 

 this construction that has quitted a French port for a distant ex- 

 pedition. Intelligence has been received of her safe arrival at 

 the place of her destination. 



VARIATION OF THE MAGNETIC NEEDLE. 



Ill our 53d Volume, p. 387, we mentioned that the excellent 

 and unremitting observations of Colonel Mark Beaufoy, made at 

 Bushey- Heath, near Stanmore, in Middlesex, had shown that the 

 magnetic variation to the westward of the true north Iiad uni- 

 formlv increased, on taking the means monthly, imtil the begin- 

 ning of the last year, after which it had fluctuated, but giving a 

 mean variation of 24° 37' 0" in the first three months of 1819. 

 The observations since published by the Colonel in a contempo- 

 rary Journal, seem to show that this was the maximum varia- 

 tion, occwvnn^'ni February or March 1819: because he finds 

 the monthly means, since the beginning of April of that year, 

 to have uniformly decreased. It further appears from the Co- 

 lonel's statements, that the western variation had been on the 

 increase through 162 years, or since 1657 : it was only 77 years 

 before this ))eriod that the first authentic observations on the 

 variation chu be found, or in 1580, when the needle at London 

 varied to the east 11° 15'. 



MARINE THERMOMETER. 



From many experiments made of late years by scientific per- 

 sons, there seems every reason to believe that the thermometer 

 is an instriunent of far greater importance to navigators than it 

 has been generally supposed. 



The late celebrated Dr. Franklin was the first person who no- 

 ticed the great difference between the temperature of the water 

 on the North American coast, on and off soundings, and sug- 

 gested the use of a thermometer as an indicator of an approach 

 to that dangerous shore, as it had been uniformly found that 

 the nearer any vessel ap]noximated the shore, the colder the tem- 

 j)erature of the water became. 



Afterwards Col. .Jonathan Williams, of Philadelphia, endea- 

 voured with some success to call the attention of seafaring men 

 to the importance of the thermometer as a nautical instrument; 

 and satisfactorily succeeded in showing that no vessel on board 

 of which a thermon^eter is, can possibly be cast away on the coasts 



of 



