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Verification of Instruments.—­On arriving at the sea-level, make daily observations with your boiling-point thermometer, barometer, and aneroid, as they are all subject to changes in their index-errors.  As soon as you have an opportunity, compare them with a standard barometer, compare also your ordinary thermometer and azimuth-compass with standard instruments, and finally, have them carefully re-verified at the Kew observatory on your return to England.  A vast deal of labour has been wholly thrown away by travellers owing to their neglecting to ascertain the index-errors of these instruments at the close of their journey.  A careful observer ought to have eliminated the effects of instrumental errors from his sextant observations; nevertheless it will be satisfactory to him, and it may clear up some apparent anomalies, to have his entire instrumental outfit re-verified at Kew.

Observations, to recalculate.—­Send by post to England a complete copy (always preserve the originals) of all your astronomical observations, that they may be carefully recalculated before your return, otherwise a long period may elapse before the longitudes are finally settled, and your book may be delayed through the consequent impossibility of preparing a correct map.  The Royal Geographical Society has frequently procured the re-calculation of observations made on important journeys, at the Royal Greenwich Observatory and elsewhere.  I presume that a well-known traveller would never find a difficulty in obtaining the calculations he might desire, through the medium of that Society, if it was distinctly understood that they were to be made at his own cost.

Lithograph Maps.—­It may add greatly to the interest which a traveller will take in drawing up a large and graphic route-map of his journey, if he knows the extreme ease and cheapness with which copies of such a map may be multiplied to any extent by a well-known process in lithography:  for these being distributed among persons interested in the country where he has travelled, will prevent his painstaking from being lost to the world.  Sketches and bird’[S-eye views may be multiplied in the same manner.  The method to which I refer is the so-called Anastatic process; the materials can be obtained, with full instructions, at any lithographer’s shop, and