of mercury, about the size of a small shot, which rub gently over the tinfoil until it spreads itself and shows a silvered surface, gently add sufficient mercury to cover the leaf so that its surface is fluid. Prepare a slip of paper the size of the tinfoil. Take the glass in the left hand, previously well cleaned, and the paper in the right. Brush the surface of the mercury gently to free it from dross. Lay the paper on the mercury, and the glass on it. Pressing gently on the glass, withdraw the paper. turn the glass on its face, and leave it on an inclined plane to allow the mercury to flow off, which is accelerated by laying a strip of tinfoil as a conductor to its lower edge. The edges may, after twelve hours' rest, be removed. In twenty-four hours give it a coat of varnish, made from spirits of wine and red sealing-wax. It may be as well to practise on small bits of common glass, which will soon prove the degree of perfection which the operator has attained." (Admiral Sir E. Belcher.)
MEMORANDA AND LOG-BOOKS.
Best form for Memoranda.--I have remarked that almost every traveller who is distinguished for the copiousness and accuracy of his journals, has written them in a remarkably small but distinct handwriting. Hard pencil-marks (HHH pencils) on common paper, or on metallic paper are very durable. Dr. Barth wrote his numerous observations entirely in Indian-ink. He kept a tiny saucer in his pocket, rubbed with the ink; when he wanted to use it, he rubbed it up with his wetted finger-tip, or resupplied it with fresh ink, and filled his pen and wrote. Captain Burton wrote very much in the dark, when lying awake at night; he used a board with prominent lines of wood, such as is adopted by the blind. It is very important that what is written should be intelligible to a stranger after a long lapse of time. A traveller may die, and his uncompleted work perish with him; or he may return, and years will pass by, and suddenly some observations he had made will be called in question.
Professor J. Forbes says:--"The practice which I have long adopted is this:--to carry a memorandum-book with Harwood's prepared paper" (in this point of detail I do not concur; see next paragraph) "and metallic pencil, in which notes and observations and slight sketches of every description, are made on the spot, and in the exact order in which they occur. These notes are almost ineffaceable, and are preserved for reference. They are then extended, as far as possible, every evening with pen and ink, in a suitable book, in the form of a journal; from which, finally, they may be extracted and modified for any ultimate purpose. The speedy extension of memoranda has several great advantages: it secures a deliberate revision of observations, whether of instruments or of nature, whilst further explanation may be sought, and very often whilst ambiguities or contradictions admit of removal by a fresh appeal to facts. By this precaution, too, the risk of losing all the fruits of some weeks of labour, by the loss of a pocket-book, may be avoided."
It has occurred to me, frequently, to be consulted about the best was of keeping MSS. Captain Blakiston, who surveyed the northern part of the Rocky Mountains, and subsequently received the medal of the Royal Geographical Society, for his exploration and admirable map of the Yang-tse-Kiang, in China, paid great attention to the subject: he was fully in possession of all I had to say on the matter; and I gladly quote the method he adopted in North America, with slight modifications, according to the results of his experience, and with a few trivial additions of my own. For the purposes of memoranda and mapping data, he uses three sets of books, which can be ordered at any lithographer's:--
No. 1. pocket Memorandum Book, measuring three inches and a half by five, made of strong paper. (Captain Blakston did not use, and I should not advise travellers to use, "prepared" paper, for it soon becomes rotten, and the leaves fall out; besides that, wet makes the paper soppy.) The books are paged with bold numbers printed in the corners; two faint red lines are ruled down the middle of each page, half an inch apart, to enable the book to be used as a field-surveyor's book when required. In this pocket=book, every single thing that is recorded at all, is originally recorded with a hard HHH pencil. Everything is written consecutively, without confusion or attempt to save space. There may easily be 150 pages in each of these books; and a sufficient number should be procured to admit of having at least one per month. Do not stint yourself in these.
No. 2. Log-Book.--This is an orderly way of collecting such parts of the surveying material as has been scattered over each day in your note-book. It is to be neatly written out, and will become the standard of future reference. By using a printed form, the labour of drawing up the log on the one hand, and that of consulting it on the other, will be vastly diminished. I give Captain Blakiston's form, in pages 28, 29, and I would urge intending travellers not to depart from it without very valid reasons, for it is the result of considerable care and experience. The size in which the form is printed here is not quite accurate, because the pages of this book are not large enough to admit of it, but the proportion is kept. The actual size is intended to be five and a half inches high and nine inches wide, so that it should open freely along one of the narrow sides of the page, in the way that all memoranda books ought to open. Four pages go to a day; of these the pages 1 and 2 are alone represented in this book, pages 3 and 4 being intended to be left blank.
The bold figures 17 and 18 in the right-hand corners of the form I give, show how the pages should be numbered. The lines in p. 18 should be faint blue.
No. 3. Calculation Book.--This should be of the same size and shape as the Log Book, and should contain outline forms for calculations. The labour and confusion saved by using these, and the accuracy of work that they ensure, are truly remarkable. The instruments used, the observations made, and especially the tables employed, are so exceedingly diverse, that I fear it would be to little purpose if I were to give special examples: each traveller must suit himself. I will, therefore, simply make a few general remarks on this subject, in the following paragraph.
Number of Observations requiring record.--A traveller does excellently, who takes latitudes by meridian altitudes, once in the twenty-four hours; a careful series of lunars once a fortnight, on an average; compass variations as often; and an occulation now and then. He will want, occasionally, a time observation by which to set his watch (I am supposing he uses no chronometer). He ought therefore to provide himself with outline forms for calculating these observations, even if he finds himself obliged to have them printed or lithographed on purpose; and in preparing them, he should bear the following well-known maxims in mind:--
Let all careful observations be in doubles. If they be for latitudes, observe a star N. and a star S.; the errors of your instruments will then affect the results in opposite directions, and the mean of the results will destroy the error. So, if for time, observe in doubles, viz., a star E. and a star W. Also, if for lunars, let your sets be in doubles--one set of distances to a star E. of moon, and one to a star W. of moon. Whenever you begin on lunars, give three hours at least to them, and bring away a reliable series; you will be thus possessed of a certainty to work upon, instead of the miserably unsatisfactory results obtained from a single set of lunars taken here and another set there, scattered all over the country, and impossible to correlate. A series should consist of six sets, each set including three simple distances. Three of these sets should be to a star or stars E. of moon, and three to a star or stars W. of moon. Lunars not taken on the E. and W. plan are almost worthless, no matter how numerous they may be, for the sextant, etc., might be inaccurate to any amount, and yet no error be manifest in their results. But the E. and W. plan exposes errors mercilessly, and also eliminates them. One of the best authorities on the requirements of sextant observations in rude land travel, the Astronomer Royal of Cape Town, says to this effect:--"Do not observe the altitude of the star in taking lunars, but compute it. The labour requisite for that observation is better bestowed in taking a large number of distances." So much delicacy of hand and of eyesight is requisite in taking lunars that shall give results reliable to seven or eight miles, and so small an exertion or flurry spoils that delicacy, that economy of labour and fidget is a matter to be carefully studied.
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