308 On a np'w Sextant rccenlli/ invented 



from the 26th March to the 1 7th September ; and under the 

 equator they can never be used for this purpose. It is on this 

 account that M. Ducom in his Course of Nautical Observations, 

 &c. Bourdeaux 1820, page 94-, in making his remarks on the 

 method of determining latitudes by ?20M-?Henc//an altitudes, says, 

 " This application may be of indispensable utility when we want 

 to find the latitude of a place, and where the meridian altitudes 

 are too great for an artificial horizon." 



This is not the case with respect to the sector of Amici; with 

 this instrument we may take the double meridian altitudes of tlie 

 sun under the tropics and even at the zenith. When M. 

 Amici came to Genoa in May to bring us his reflecting sector, 

 we could no longer at that time take in the artificial horizon 

 meridian altitudes of the sun with any of our sextants, which, 

 however, M. Amici was able to do with his sextant. On the 

 17th and 18th of May he took thirteen circum-meridian alti- 

 tudes of the Sim ; we shall here mention only those made at 

 noon. The 1 7th of May the altitude of the superior limb of the 

 sun was = 64° 56' 20"; the 18th of May, = 64° 38' 10", error of 

 collimation + lO' 50". These observations, with a number of 

 others since made towards the summer solstice, have always 

 given us, within a few seconds, the latitude marked in our little 

 observatory. 



We could here enumerate many other advantages ; as for ex-. 

 ample, that we can verify upon this sector the pomt zero, and 

 the pomt 90 deg., as has been seen in the descri})tion : That in 

 taking altitudes on an artificial horizon, the telescope always 

 rests in a horizontal position, so that the observer may sit at his 

 ease before it, without changing the position either of his body 

 or head, whatever be the altitude of the star he is observing : 

 That at sea we may take all the altitudes of two opposite hori- 

 zons, the anterior and posterior, the mean of which will correct 

 the mirage and all other irregularities of the refraction: but on 

 these subjects we shall attaui more knowledge and experience 

 when M. Amici has finished a large 1 2-inch sector of reflection, 

 which he has in hand at present, and to which he will adapt all 

 those impi'ovements which the use and practice of this instru- 

 ment have suggested to him, during the stay which this inge- 

 nious and much-esteemed philosopher made with us. 



The small 4-inch sector, which M. Amici has above de- 

 scribed, and which is the first that was ever made, is now in 

 our possession, and we habitually use it in taking corre- 

 spondent altitudes of the sun. We are both proud and jealous 

 of being possessed of the first model of so fine an invention ; 

 which, like all other useful novelties, will require time to make 

 way through, and get ritl of, ancient modes and usages, which 



throii'fh 



