62 Mr. Forbes's Determination of the. Geographical Positions 



the instrument east and half west. The piercing cold of the 

 night rendered these observations somewhat difficult, being 

 a transition of no less than 60° Fahrenheit, from the heat 

 under which I had been suffering in the plain a few days be- 

 fore. The longitudes which I have deduced chronometrically 

 cannot of course be depended upon to great exactness, con- 

 sidering the trial to which the instrument is subjected in tra- 

 velling on the mountains. The rates which I shall give below 

 will show the degree of confidence which may be placed upon 

 them. The chronometer was constructed for me with extreme 

 care by Mr. Whitelaw, of Edinburgh, an artist whose inge- 

 nuity and practical skill will, I hope, in due time be generally 

 appreciated*. I have been perfectly satisfied with the per- 

 formance of this instrument, under a great variety of trials to 

 which it has been subjected : the rates I am about to give 

 w T ere influenced of course by the incessant jolting of a very 

 rough journey, made chiefly on foot, and are only to be con- 

 sidered in reference to such circumstances. 



Geneva, 1832. — Mean daily rate of chrono-1 OQs.a 

 meter, August 16 — 18 J 



From August 18 to September 5 (including! _ fi ^ 

 the journey in Savoy). 3 



From September 5 to September 6 +26 '0 



Chamouni. — From August 24 to August 26... +26 *1 

 N.B. This uniform rate is surprising, when I state that in 

 the interval (August 25) I made the excursion to the "Jardin," 

 with the chronometer in my pocket. I should certainly have 

 left it behind, had I not required it for magnetical observa- 

 tions which I made at the " Jardin." 



Observations. 

 Geneva, Aug. 18 d h . Error of chronometer upon mean 



time at the Observatory slow ll m 46 s, 2. 



Chamouni. Le Prieure. Aug. 24 d 4 h 31 m . Error of chro- 

 nometer upon mean time by eight simple altitudes of 

 the sun ; four with the limb of the instrument in each 



direction slow 12 m 10 s *0 



Aug. 26 d 4 h 4S m . By five simple altitudes slow 11 17 *8 



Aug. 26. Determination of the latitude by altitudes of Polaris. 

 Time by Chron. Face of Instrument. Altitude. Latitude. 



ll h 18 m 27 s '5 West. 46° 59' 30" 45°55' 14" 



40 19 East. 47 7 30 45 56 40 



47 49 East. 47 9 22 45 56 26 



* A description of his beautiful escapement has been given by Mr. Ro- 

 bison in the Edinburgh Transactions, vol. xi. 



