« PoprzedniaDalej »
pressure at sea, two barometers are necessary, one for calm and another for stormy weather. Whether our merchant sailors will accept the assistance liberally offered to them may be doubtful, but should these perfect instruments be introduced, either by choice or compulsion, the sailor will derive a future as well as a present advantage from the investigation; and the log book, which is now, in too many instances, a worthless document when the voyage is ended, will bPcome a valuable book to the man of science, from which new facts may be gathered for the benefit and security of future navigators. That these labours would be appreciated by the governments of great commercial nations was to be expected ; and prudence suggested the necessity of immediately introducing the improved instruments into their navies. In this instance
there has been no delay on the part of naval authorities. The Kew Committee have, at the present time, for verification, a large number of thermometers and barometers, constructed under its superintendence, for our own Board of Trade and the navy of the United States.
The commercial interests common to England and America necessarily produce a community of motive in scientific research, and a participation in the benefits resulting from it. This is especially the case in all that concerns the navigation of the ocean. England performs an imperative duty, as well as an act of friendship, in testing the marine barometers and thermometers of America. For this we can take no credit to ourselves, as it is only an acknowledgment to the United States that we have been benefited by her example and labour. It may not be known to some of our readers that the American government has been for some years actively and systematically collecting and arranging information from all credible sources relating to the winds, tides, currents, and temperature of the ocean. The direction of this inquiry was entrusted to Lieut. Maury, who suggested it. By the ready assistance he received from the mercantile marine of his own country, he has been able to supply the sailors of all nations with a variety of charts and printed records which have done much to give security to the navigation of the seas they describe. While receiving this lesson in practical science from a nation whose energy in enterprise and patience in research, we, of all other people, have most reason to applaud, it is well that the debt should not be forgotten. There never will be a time, we hope, when England will refuse, either from indolence or pride, to assist in any effort which may be made to save life, protect property, or to advance the intellectual and religious freedom of man. The blessings we enjoy and the holy mission we have received from the Most High, demand an acknowledgment in labour which shall have
a higher motive than personal interests or national jealousy. While, therefore, we present to America the barometers and thermometers which have been verified for her navy, we acknowledge our obligations to that well-devised and successfully-pursued scheme which has roused the government of England to an acknowledgment of the necessity of doing something for the improvement of navigation and the safety of commerce. Prompted by men of science who have felt the disgrace of receiving the benefit without participating in the labour of research and experiment, the British government has established a scientific department in connexion with the Board of Trade, the business of which will be similar to that over which Lieut. Maury presides in America. Captain Fitzroy, who is, according to the Earl of Harrowby, 'the one man best fitted to carry out with energy and success the objects of this department, has been placed at its head. The high praise he has received from his friends will, no doubt, strengthen his determination to perform the duties he has accepted, and thus to satisfy the hopes and deserve the praise of those who welcome him to office. But while it is easy to pardon the injudicious zeal of friends, we must blame every attempt to get credit for what is to be done by finding fault with that which has been done. If it be true that the documents hitherto published by Lieut. Maury present too much detail to the seaman's eye,—that they have not been adequately condensed, and therefore are not practically so useful as is supposed,'—if all this be literally true, Captain Fitzroy should not have said it until he had something more than promises to give in return for the documents and suggestions he has received. When, by the collection of data, he is able to prepare a number of conveniently-arranged tabular books,' from whích, 'at a subsequent period, diagrams, charts, and meteorological dictionaries or records shall be compiled, so that by turning to the latitude and longitude all information about the locality may be obtained at once and distinctly,'—then the public will fairly estimate the value of the labours of Captain Fitzroy, and award him the honour he deserves. That he would, under any circumstances, prove himself an efficient and useful officer there is no doubt; but he has created for himself new motives for exertion in the pledges he has given, for his countrymen will demand their redemption.
But we should not deal fairly with Captain Fitzroy if we left our readers to imagine from one injudicious expression that he altogether undervalues the labours of Lieut. Maury, in comparing them with his intended future performances. In another place he has dealt more generously with his own reputation and the honours of his predecessor.
The success of the experiments to be now made by British and and American navigators under the direction of scientific governmental departments respecting the weight and temperature of the sea and atmosphere, depends chiefly upon the accuracy of the instruments of observation - upon the possession of barometers and thermometers which tell the truth everywhere. The storm makes its coming known on the mercury of the haroineter before it bursts on the ship, bowing its proud streamers to the crests of the mountain waves. The floating ice-island sends a chilly stream as the herald of its coming, and the thermometer does not interrogate it in vain, when it returns with its message to the hand of an intelligent mariner. The sailor can no more plough the highways of the ocean without the barometer and thermometer than a surveyor can register the lines of an intended railroad without chain and level. But something more is wanted for safe travelling upon the ocean highways. The sailor must have guides to lead him to them, and to prevent him from straying. For this purpose, the chronometer and the compass are required ; and we must now see what science says about their qualifications, and by what means it hopes to make them more fit for the duties they have to perform.
When the British Association met at Liverpool, in 1837, the committee presented a memorial to the town council of the borough recommending the establishment of a nautical observatory; and among the duties which, in their opinion, should be undertaken by such an institution, that of receiving and rating chronometers was particularly mentioned. The recommendation of the scientific authorities was favourably received by the town council, and an observatory was soon after established. The management of this excellent institution was entrusted to Mr. Hartnup, of whose labours we can say no less than that they have done honour to the united scientific and commercial spirit which they represent. At the last meeting of the Association, held in the same town, Mr. Hartnup reminded the members of the part they had taken in the establishment of the cbservatory, and presented them a report of what he had been able to accomplish. By the objects of the establishment, and the recommendation of the Association, his attention had been drawn to the study of chronometers, and to the correction of those errors in rate which arise from a change of temperature. The importance of this subject and the results of his labour we will endeavour to explain.
A chronometer is used at sea to find the longitude. When this indispensable instrument is given to the commander of a ship he is told its rate; that is to say, what it gains or loses daily, that he may make the necessary corrections. Now when it is
remembered that an error of seven seconds a-day will in eighteen days make one of more than two minutes, and that the loss or gain of two minutes may endanger a ship and all it contains, there is no need of argument to prove the necessity of knowing the sources of error, and of determining the amount. It sometimes happens that merchant-vessels have chronometers which are altogether untrustworthy; instruments so bad in construction or adjustment, that the crime of deception, in a matter affecting life as well as property, must be charged against the maker, and culpable ignorance or inattention against the buyer. With these defective and useless instruments the rater has nothing to do; they are excluded altogether from the range of his experiments. But taking the average quality of the chronometers received by merchant-vessels (and they are for the most part inferior to those accepted by the navy), it is important to determine what circumstances affect their rate, and what is the average of their loss or gain. Some errors arise from circumstances which are not understood; such as a change of place from sea to land, and from one hemisphere to another. All that we at present know is, that “the average of the sea rates of chronometers employed in the American trade agrees with the rates of the same chronometers on shore in a temperature of about 60°, and that 'the average of the sea rates of chronometers which have been exposed to a tropical climate during a great part of the voyage agrees with the rates of the same chronometers on shore in a temperature of about 80°
But there is another still more important source of error which is understood, and which may be corrected—that resulting from a change of temperature. To this subject Mr. Hartnup has given his attention, and the results of ten years' experience are before us. The average change of rate in the chronometers employed by the merchant service, for a change of temperature from 40° to 60° Fahrenheit, is, he says, seven seconds a-day; and this, as already stated, may be a dangerous error.
“This variation of rate,' says Mr. Hartnup, differs so much in different time-keepers, that, without a trial, no idea can be formed of its amount in any particular chronometer. In order to show this more clearly, we have compiled from the records of the Observatory three tables : each table shows the change of rate for each of one hundred chronometers, caused by changing the temperature to the extent named in the respective headings. In Table 1 the average change in the daily rate, caused by changing the temperature from 40° to 60° is,6:97". Taking the two extremes, one chronometer in the hundred gained 15-3", and one lost 72.2" a-day, by changing the teme perature only 20°. The average change of rate of the first ten in the hundred is 7.1" gaining ; the average of the second ten is 0-3" losing; and the average of the last ten in the hundred is 29.8" losing. Tables 2
and 3 show the change of rate caused by changing the temperature from 60° to 80°, and from 50° to 80° respectively, and it will be seen that the variations were much greater in the low than in the high temperatures.'
It is scarcely possible to read this report without believing that we have found the reason why accidents at sea are so frequent. That they are frequent everybody acknowledges, but the statistics are comparatively unknown. A few figures connected with this subject will create a deeper interest in the efforts science is now making to improve the art and increase the profits of maritime navigation. From an analysis of the reports made to Lloyd's of the casualties to sailing vessels at sea during the four years ending 1850, we find that of the gross number (12,041) no less than 5117 were occasioned by vessels being driven on shore, 2665 by collision, and 2295 by wreck; while 204 sailed, and were lost, without leaving a hand to record the destruction. It is appalling to think that even, according to these figures, and they state only a part of the casualties, there is, on the average, an accident at sea once every three hours, by night and by day. The loss of life and property is not correctly known, and the estimated number and amount is so great, that we can scarcely believe the results of our calculations. But it would be of incalculable benefit if we could obtain the statistics of causes—how many arose from ignorance of the rate of the chronometer, how many from the deflection of the compass, and what number were injured or lost because they were not forewarned by the barometer or thermometer. That the want of correct instruments is a fruitful cause in the production of these accidents may be gathered from the fact that they have happened chiefly to vessels between 90 and 500 tons burthen, for only 64 of the whole number of accidents are attributed to vessels of 700 tons and upward. The smaller the vessel-speaking in general terms, and of a class—the more imperfect are the instruments of observation, and the less is the complement of men in proportion to the tonnage; while the general arrangements for comfort and security are below the average of the trade in which the vessel is engaged. There is, therefore, good reason to believe that a large proportion of accidents will fall upon this class of vessels, and that as much of the evil may be traced to defect of instrument as to want of knowledge ; in fact, they go hand in hand, to the destruction of life and property. Skill and seamanship are prime qualities in the estimation of safety at sea ; but a good seaman depending on bad instruments is like a gipsy guide on a burning heath, when his beacons are a part of a general conflagration.
Mr. Hartnup has done good service to our merchants and their seamen by ascertaining the amount of error to which chronometers