1...

gave the difference of longitude of the two places in hours, which was reduced to distance as above stated.

Next follow detailed directions for finding the North star by means of the pointers or guards as they were called, and also for determining the latitude and the local time by observations of this star. To effect this there was given a table showing the degrees and minutes to be added to or subtracted from the altitude of Polaris according to the compass bearing of the pointers from the star; this correction was given for the four cardinal and four intercardinal points. To enable this correction to be found more accurately, an instrument called the Rectifier of the North Star was devised: this was the invention of Cogniet so often quoted in the text and was quite an elaborate affair: under ordinary circumstances it might produce tolerably accurate results. It consisted essentially of a compass card containing at each point the degrees and quarters of a degree to be applied to the altitude of the star according to the bearing of the pointers: a ruler turned upon a hollow spindle in the centre, through which the line of sight passed. When in use, the instrument was raised in front of the face by means of the handle (which was situated at the south point) until the star was visible through the central spindle: the ruler was then moved until the nearest pointer could be seen in line with it and the correction was read off the arc where the ruler intersected it. Directions are also given for using any other star than the nearest pointer, provided the difference of right ascensions was known. This instrument was also used as a Nocturnlabe or determiner of time at night: the inner circle of the compass card was divided into three hundred and sixty five equal parts, which were named and numbered according to the number of days in each month, the days upon which the star crossed the meridian at noon and midnight being placed opposite the North and South points respectively: a small circle divided into twenty-four equal parts or hours moved also upon the central pivot, and the twelve hour mark was placed opposite the day of the month before using the instrument: the reading of the point at which the ruler before mentioned cut the hour circle gave the hour of the night. Provided that the North and South line could be held in the plane of the meridian, this instrument would give very good results. The concluding chapters of the work are devoted to the subject of tides and the finding of the time of high water.

From this brief glance, we see that the mariner of three centuries ago was able to obtain results, which only by a very liberal stretch of the term could be called approximative. With the instruments at his disposal,

it could not have been possible to obtain the altitude of the sun within twenty minutes: to say nothing of the probable error of the declination owing to want of proper tables, there were no corrections made for semi-diameter, dip or refraction, and hence the latitude could not have been reliably determined within thirty minutes; probably if the result came within forty or forty-five minutes of the true one, it would be doing very well. As upon the determination of the latitude rested, as we have seen, the subsequent approximation to the distance and difference of longitude made good, it follows that these latter results must have been very far from the truth. And yet, before the close of the sixteenth century, even with such inferior means of determining the ship's position, the great voyages of discovery had been made. Prince Henry the Navigator had largely increased the existing knowledge of the west coast of Africa; Vasco de Gama had rounded the Cape of Good Hope and the African continent had been circumnavigated; Columbus had brought to light the New World; Cabot and a host of others had followed in his foot steps; Balboa had crossed the Isthmus of Panama and discovered the Pacific Ocean; Magalhaens bad discovered the strait that still bears his name and sailing through it had entered the Pacific Ocean; stretching boldly across which, he reached the Philippine Islands, his vessel being the first to accomplish the circumnavigation of the globe.

Commander W. T. SAMPSON, U. S. N., in the Chair.

No. 5.

PRESERVATION OF WOOD.

BY PROF. CHAS. E. MUNROE, U. S. N. A.

Mr. Chairman, Gentlemen,

Wherever life exists we find a constant struggle for its maintenance. In every animal and vegetable substance, so soon as the vital force ceases to act, we see that there is at once a tendency toward the resolution of the atoms of the highly organized structure into simpler compounds. All nature seems to lend its aid to effect this change. The chemical affinities of the constituent substances encourage it, the lower forms of life assist it, and the combined influence of air, moisture and heat complete the change. Everywhere these forces are active and decay and destruction threatens.

All of the products of life which we employ either for food or clothing or for constructing our habitations, our ships, or our tools are exposed to this danger; and one of the most important industrial problems, which man has had to meet, has been the protection of these substances from decay.

It is my intention to-night to confine myself to an examination of the methods proposed for the preservation of one of these substances, wood, and especially as it is employed in ship-building. Though it may seem unnecessary to you that I should give any statistics to show the great value of employing some means for attaining this result, yet

it will I believe impress the importance of it more strongly upon our minds if we give a moment to their consideration.

The first fact which attracts our attention is the rapid destruction of our forests which is diminishing the supply and increasing the cost of lumber. While, for instance, a single acre of pine land yields on an average only six thousand feet of timber, billions of feet are annually sold in the United States. In 1855 lumber sold for about $18 per M.; in 1860, for $24; and in 1865 for $45, (Hunt's Merchant's Mag. Feb. '66, p. 106). Excellent authority states that in New England the cost of oak, ash and hickory has doubled during the past twenty years, being now $50 per M., to $ 25 then, and if the demand were as great as ten years ago it would be difficult to supply it. Certainly prudence demands a less rapid expenditure.

But when we come to estimate the loss, which results from decay, the necessity for preservation becomes still more apparent. It was calcu- . lated in 1866, that the loss by the decay of sleepers on American Railroads, amounted annually to $ 1056 pr. mile, and that if they were preserved by cupric sulphate at a light expense there would be an annual saving of over $ 4,000,000, (Lewis) and if we included bridges and all the wooden parts of railways subject to decay, it is stated that $20,000,000 would be saved annually, by impregnating them with coal tar (Robbins p. 67). Processes have been devised by which the durability of many kinds of wood can be doubled; hence if we consider how much timber is employed in the United States alone, in buildings, bridges, fences, ships, carriages and machines, we can readily see that' a great saving would be effected, that our wealth would be increased, and that a large part of the labor, which is now employed in making good the losses from decay, could be used in production.

It is more to our purpose, however, and it was my desire, to collect some statistics concerning the decay of ships; but such as I have obtained are quite meagre and unsatisfactory.

In 1833 Mr. Edye, (Calculations relating to the Equipment of Ships by John Edye, London), stated that the quantity of wood required aunually to keep the five hundred and seventy four ships of the British Navy seaworthy was one hundred and twenty five thousand loads, while only one million loads was required to build them-twelve and one half per cent. Mr. Wm. Chapman, (Preservation of Timber from premature decay, &c., by Wm. Chapman), gives several instances of the rapid decay of ships of the Royal Navy about the commencement of the present century. He mentions three ships of seventy four guns decayed in

five years, three of seventy four guns decayed in four years, and one of one hundred guns decayed in six years. Pering, (Brief Enquiry into the causes of the Premature Decay), says that ships of war are useless in five or six years. And he estimates the average duration to be eight years, and that the cost of the hull alone of one of these ships was nearly £100,000.

When we come to our own service we find that here also the loss by decay is enormous. Our live oak ships are exceptional, their average life being, probably, a half century, but I find from an examination of the data given by Emmons (p 23 and 86, et seq.,) that the average cost per ton per year for repairs, was $ 6.00 amounting in the case of a vessel like the Ohio to $ 16,569.57. Up to 1850 the Ohio cost for repairs $ 471,673.* If now we estimate the loss upon the basis of actual sea service we find that the average cost per ton (O. T.,) per year of service was $16.19. The cost of repairs to the Ohio per year of service was over $89,000, and the United States, Potomac, Brandywine &c., average about $35,000 while the Constitution, which was an exceptionally good ship, cost over $ 15,000 per year of service.t

To gather any information about our present Navy is more difficult, and we must wait for some one to record for it what Emmons has so thoroughly done for the Navy previous to 1850. Such as we do find however shows that of late the loss from decay is greater than before. We find vessels built of white oak costing from a quarter of a million to over a million dollars thoroughly useless in eight to ten years. Indeed this is a large estimate, for it is stated by some authorities that the average age of a white oak ship is six years. The difficulties met with in getting any certain knowledge on the subject are best shown by the following extract from a letter from the late chief of the Bureau of Construction and Repairs, Chief Naval Constructor I. Hanscom. He says, "I believe you will only be able to obtain approximate data as to the relative durability of Live and White Oak, White and Yellow Pine timber, as it varies so much, caused by the difference in quality and degree of preservation, either by stowage or by the use of chemicals, that the condition of the timber at the time of using it can hardly be known. Still the contrast in the durability of the timber used in the construction of the "Franklin" and that of the "Delaware "-the former in good condition at the present time (twenty three years), and the latter generally rotten in eight years, each costing nearly the same, * While the cost of building her was only $547,889.

† See Appendix.