applying the requisite corrections when necessary, and one or more of them should be compared with the standard instruments at the Royal Society or Royal Observatory on your return home.
6. All observations which involve the comparison of minute differences, should be the mean result of at least three readings, and should be as much as possible the province of the same individual observer.
7. In some of those singularly heavy showers which occur in crossing the equator, and also at the changes of the monsoon, an attempt should be made to measure the quantity of rain that falls in a given time. A very rude instrument, if properly placed, will answer this purpose; merely a wide superficial basin to receive the rain, and to deliver it into a pipe whose diameter, compared with that of the basin, will show the number of inches, &c., that have fallen, on an exaggerated scale.
8. It is unnecessary to call your attention to the necessity of recording every circumstance connected with those highly interesting phenomena—the Aurora Australis and Borealis; such as the angular bearing and elevation of the point of corruscation; the bearing also of the principal luminous arches, &c. &c.
9. It has been asserted that lunar and solar halos are not always exactly circular; and a general order might therefore be given to the officer of the watch to measure their vertical and horizontal diameters whenever they occur.
Large collections of natural history cannot be expected, nor any connected account of the structure or geological arrangement of the great continent which you are to coast; nor indeed would minute inquiries on these subjects be at all consistent with the true objects of the survey. But at the islands, and even along the
