small angles under which very remote moun

tains appear;

A sextant by Ramsden, of ten inches radius, with a silver limb, and telescopes which magnify

from twelve to sixteen times;

A snuff box sextant by Troughton, of two inches radius, with a nonius divided into minutes, telescopes which magnify four times, and an artificial horizon of crystal. This small instrument is very useful for travellers when forced in a boat to lay down the sinuosities of a river, or take angles on horseback without dismounting;

A reflecting and repeating circle by Le Noir, of twelve inches diameter, with a mirror of platina*;

A theodolite by Hurter, the azimuth circle of which was eight inches in diameter;

An artificial horizon by Caroché, of plane glass, six inches in diameter, with an air-bubble level, the divisions of which are equivalent to two sexagesimal records;

A quadrant by Bird, with a radius of a foot, fur

nished with a double division of the limb into ninety and ninety-six degrees, the micrometer screw indicating two sexagesimal seconds;

* I have compared in another place the advantages and disadvantages, in long journeys, of the reflecting instruments and astronomical repeating circles. (Astron. Observ. Introd. t. i, p. 17.)

the perpendicularity of the plane capable of being determined by means of a plummet and a large air-bubble level;

A graphometer by Ramsden, placed on a cane, with a magnetic needle, and a wire meridian to take magnetical azimuths;

A dipping needle of twelve inches, constructed on the principles of Borda and Le Noir. This instrument, of the most perfect execution, was ceded to me, at the time of my departure, by the French board of longitude. The figure of this instrument will be found in the narrative of the voyage of d'Entrecasteaux *, the astronomical part of which was composed by a learned navigator, Mr. de Rossel. An azimuth circle serves to find the plane of the magnetic meridian, either by correspondent dips, or by seeking the position in which the needle is vertical, or observing the minimum of the dippings. The instrument is verified by observing on the east and west side, and changing the poles;

A variation compass by Le Noir, constructed on the principles of Lambert, and furnished with a wire meridian. The nonius was divided at every two minutes;

A needle twelve inches long, furnished with sight-vanes, and suspended to an untwisted thread according to the method of Coulomb.

* Vol. ii. p. 14.

This apparatus, like the magnetic telescope of Prony, served me to determine the small horary variations of the magnetic variation, and the intensity of the forces which change with the latitudes. The oscillations of the great magnetic dipping needle of Mr. Le Noir give also a very exact measure of this last pheno

menon.

A magnetometer of Saussure*, constructed by Mr. Paul at Geneva, with a limb that corresponds to an arch of three feet radius;

An invariable pendulum, constructed by Mr. Megnie, at Madrid;

Two barometers by Ramsden;

Two barometrical apparatusest, with the aid of which we find the mean height of the barometer, by successively plunging into a vessel several glass tubes, filled with mercury, closed at one end by a steel screw, and placed in a metal case;

Several thermometers by Paul, Ramsden, Megnie, and Fortin;

Two hygrometers of Saussure and Deluc, of hair and whalebone;

Two electrometers of Bennet and Saussure, of

* This magnetometer, which I found inaccurate, the theodolite, and reflecting circle, are the only instruments which I could not embark with me at Corunna.

+ I have described this apparatus in the Journal de Physique, t: xlvii, p. 468, and in my Observ. Astron. t. i, p. 366.

gold leaf and elder pith, furnished with conductors four feet long, to collect, according to the method prescribed by Mr. Volta, the electricity of the atmosphere, by means of an ignited substance which yields smoke A cyanometer by Paul. To give me the means of comparing with some certainty the blue colour of the sky, as it is seen on the summit of the Alps and the Cordilleras, Mr. Pictet had this cyanometer coloured conformably to the division of that which Mr. de Saussure made use of at the top of Mount Blanc, and during his memorable abode at the Col du Geant;

An eudiometer of Fontana, for nitrous gas; without strictly knowing how many parts of this gas are necessary to saturate a portion of oxygen, we may still precisely determine the quantity of atmospheric azote, and consequently the purity of the air, by employing, beside the nitrous gas, the oxygenated muriated acid, or a solution of sulphat of iron. Volta's eudiometer, though the most exact of any, is embarrassing for travellers, who traverse damp countries, on account of the small electric discharge, which the inflammation of oxygen and hydrogen gasses requires. The most portable eudiometrical apparatus, the most speedy and most eligible in every respect, is that pub

lished by Mr. Gay-Lussac in the memoirs of the society of Arcueil* ;

A phosphoric eudiometer by Reboul. By the

nice researches of Mr. Thenard, on charcoal mixed with phosphorus, it is proved, that the slow action of this acidifiable basis

yields

results less exact than strong combustion; An apparatus by Paul, proper to determine with the greatest precision the degree at which water boils at different heights, above the level of the ocean. The thermometer with a double nonius had been constructed from the apparatus, which Mr. de Saussure employed in his excursions;

A thermometrical lead by Dumotier, consisting of a cylindric vase, furnished with two conical valves, and enclosing a thermometer; Two areometers of Nicholson and Dollond; A compound microscope of Hofmann, described in the history of the Cryptogamiæ by Mr. Hedwig; a standard metre by Le Noir; a land surveyor's chain; an assay balance; a rain gauge; tubes of absorption to indicate small quantities of carbonic acid and oxygen, by means of lime-water, or a solution of sulphuret of potash; some Hauy's electroscopical apparatuses;

Vol. 2, p. 235. See also the memoirs in the composition of the air which I published conjointly with Mr. Gay-Lussac in the Journal de Physique, vol. lix, p. 129, and my Zoological Observations, vol. i, p. 256.

+ Bulletin of the Philomathic Society, 1812, No. 37, p. 93.