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The science of Astronomy may occasionally derive benefit from the observations of navigators, in the following respects :

By contributions to Astronomy in general.
By improvement of the methods of Nautical

By accurate attention to Astronomical Geography.
The remarks which follow will be arranged under
these heads.

General Astronomy. 1. The first point which calls for attention is the observation of the places of comets or other extraordinary bodies, especially those which can be seen only in low northern or in southern latitudes. In regard to these observations and indeed to almost all others), one remark cannot be too strongly impressed on the observers—that a bad observation, or an observation


which is given without the means of verification, is worse than no observation at all. In order to make the observations good, the following cautions must be observed :

The index-error of the sextant must be carefully ascertained. If it has not been found a short time before the observations, it must be found as soon as possible after them.

The distance of the comet from three conspicuous stars in different directions must be measured with the sextant. The point of the comet which is observed with the sextant should be precisely described. It is desirable that the navigator should be possessed of some star-maps or star-charts, by means of which he will be able at once to give the proper names to the stars, and much confusion and loss of time will be avoided.

If the time at the ship and the latitude are very well known, there will be no occasion to make further observations; but if these are not well known, some attempt must be made by the use of Becher's horizon, or by any equivalent method) to ascertain the altitude of the stars and the comet. The lower these objects are, the greater must be the care in the determination of their altitude.

For affording means of verification, these rules should be followed :

The observations of distance with the sextant should be entered in the book precisely in the manner in which they are made. The reading of the sextant, uncorrected, should be written down: in a column by the side of this should be written the correction for indexerror, with a statement whether it is to be added to, or

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