It has been suggested by some geologists, that the coral insect, instead of raising its superstructure directly from the bottom of the sea, works only on the summits of submarine mountains, which have been projected upwards by volcanic action. They account, therefore, for the basin-like form so generally observed in coral islands, by supposing that they exist on the circular lip of extinct volcanic craters; and as much of your work will lie among islands and cays of coral formation, you should collect every fact which can throw any light on the subject.
Hitherto it has been made a part of the duty of all the surveying vessels to keep an exact register of the height of the barometer, at its two maxima of 9, and its two minima of 3 o'clock, as well as that of the thermometer at the above periods, and at its own day and night maximum and minimum, as well as the continual comparative temperature of the sea and air. This was done with the view of assisting to provide authentic data, collected from all parts of the world, and ready for the use of future labourers, whenever some accidental discovery, or the direction of some powerful mind, should happily rescue that science from its present neglected state. But those hours of entry greatly interfere with the employments of such officers as are capable of registering those instruments with the precision and delicacy which alone can render meteorologic data useful, and their future utility is at present so uncertain, that it does not appear necessary that you should do more than record, twice a day, the height of the former, as well as the extremes of the thermometer, unless, from some unforeseen cause, you should be long detained in any one port, when a system of these observations might then be advantageously undertaken. There are, however, some occasional observations, which cannot fail of being extensively useful in future investigations:
1. During the approach of the periodic changes of wind and weather, and then the hygrometer, also, should find a place in the journal.
2. The mean temperature of the sea at the equator, or, perhaps, under a vertical sun. These observations should be repeated whenever the ship is in either of those situations, as well in the Atlantic as in the Pacific; they should be made far away from the influence of the land, and at certain constant depths, suppose fifty and ten fathoms, and at the surface also; and this last ought to be again observed at the corresponding hour of the night.
3. A collection of good observations, systematically continued, for the purpose of connecting the isothermal lines of the globe, and made, as above, at certain uniform depths.
4. Some very interesting facts might result from the comparison of the direct heat of the solar rays in high and low latitudes. The two thermometers for this purpose should be precisely similar in every respect; the ball of the one should be covered with white kerseymere, and of the other with black kerseymere, and they should be suspended far out of the reach of any reflected heat from the ship, and also at the same elevation above the surface of the water; the observations should be made out of sight of land, in a variety of latitudes, and at different hours of the day, and every pains taken to render them all strictly similar and comparative.
5. All your meteorologic instruments should be carefully compared throughout a large extent of the scales, and tabulated for the purpose of 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, attempts 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 mouth of the basin, will show the number of inches, etc. that have fallen on an exaggerated scale.
8. It is unnecessary to call your attention to the necessity of recording every circumstance connected with that highly interesting phenomenon, the Aurora Australis, such as the angular bearing and elevation of the point of coruscation; the bearing also of the principal luminous arches, etc.
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, day or night.
Large collections of natural history cannot be expected, nor any connected account of the structure or geological arrangements of the great islands 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, to an observant eye, some facts will unavoidably present themselves, which will be well worth recording, and the medical officers will, no doubt, be anxious to contribute their share to the scientific character of the survey.
I have now exhausted every subject to which it can be necessary to call the attention of an officer of your long experience; and I have, therefore, only further to express my conviction, that if Providence permits you to retain your wonted health and activity, you will pursue the great objects of this expedition with all the energy in your power, and with all the perseverance consistent with a due regard to the safety of His Majesty's Ship, and to the comfort of your officers and crew.
Given, etc. this 8th of June, 1837.
F. Beaufort,
Hydrographer.
* * * * *
OFFICERS AND CREW.
The crew embarked in the Beagle in this her third voyage, consisted of:
John Clements Wickham, Commander and Surveyor.
James B. Emery, Lieutenant.
Henry Eden, Lieutenant.
John Lort Stokes, Lieutenant and Assistant Surveyor.
Alexander B. Usborne, Master.
Benjamin Bynoe, Surgeon.
Thomas Tait, Assistant Surgeon.
John E. Dring, Clerk in charge.
Benjamin F. Helpman, Mate.
Auchmuty T. Freeze, Mate.
Thomas T. Birch, Mate.
L.R. Fitzmaurice, Mate.*
William Tarrant, Master's Assistant.
Charles Keys,** Clerk.
Thomas Sorrell, Boatswain.
John Weeks, Carpenter.
A corporal of marines and seven privates, with forty seamen and boys.
(*Footnote. This officer I afterwards appointed to the assistant surveyorship (vacated upon my succeeding Captain Wickham) on account of the active part he had taken in the surveying duties: an appointment most handsomely confirmed by Captain Beaufort.)
(**Footnote. Mr. Keys was always a volunteer for boat work, and is entitled to honourable mention as being, even where all were zealous, of great value upon more than one occasion.)
During our six years' voyage the following changes occurred:
Mr. Usborne invalided, in consequence of his wound, in May 1839; Mr. Birch exchanged, in August 1839, with Mr. Pasco, into the Britomart; Mr. Freeze exchanged, in September 1839, with Mr. Forsyth,* into the Pelorus; in February 1840, Mr. Helpman joined the colonial service in Western Australia; Mr. C.J. Parker was appointed, in December 1840, to Mr. Usborne's vacancy, superseding Mr. Tarrant, who had been doing Master's duty since Mr. Usborne left; Lieutenants Emery and Eden returned to England in March 1841. Late in the same month Commander Wickham invalided, when the writer of this narrative was appointed to the vacant command, by Commander Owen Stanley, H.M.S. Britomart, senior officer present, an appointment subsequently