Abstract
THE following, which has been sent us by the Scientific Editor of Harper's Weekly, shows with what minuteness the scientific work of this country is studied in America, and what a critical audience we have on the other side of the water:—One of the most important services that astronomy has rendered to mankind consists in the contributions it has made to the progress of navigation, and the increased security of life and property. In this field England has always taken the lead, and the efforts of Mr. Hartnup at Liverpool are a worthy continuation of the labours of Flarnstead, Bradley, and Airy. While the Greenwich Observatory has caused a great improvement in the general standard of the chronometers bought for the use of the Government vessels, Mr. Hartnup has sought to effect a similar reform for the mercantile marine. He has insisted on the vital importance to ship-masters, as well as to owners and insurance companies, of the careful determination of the rates of their chronometers as affected by temperature. The makers of these instruments and the astronomers who use them carefully have always known that which captains of vessels have been very slow to profit by—i.e. that the chronometers are, when made, so adjusted that they keep perfect time at two temperatures, such as 55° and 85° F., while between these limits they gain, and beyond them they lose, on the true time. It is rare that this variation in the chronometer rate can be safely overlooked by a careful navigator, though it is frequently done by those whose vessels do not carry a precious burden of 1,000 or 2,000 souls. The only excuse for this neglect is the positive assurance of the maker that the chronometer is perfectly reliable—an assurance that is often fortified by very deceitful figures. The difficulty and expense of a searching investigation into the errors to which every chronometer is liable have long been supposed by the trade to stand in the way of the introduction of such chronometers only as were of approved reliability. In order to obviate the difficulty as far as possible, the Liverpool Observatory has been constructed by Mr. Hartnup specially for the purpose of studying the rates of the chronometers that may be sent thither by captains sailing from that port. The expense of the examination given to such chronometers is comparatively trifling; and the number of chronometers submitted to him has annually increased, until by reason of the recent regulations at that port the number of examinations has amounted to between 1,000 and 2,000 annually, the same instruments having been repeatedly submitted to him. The process pursued by Mr. Hartnup consists in exposing each chronometer for a week to a uniform temperature of 55°, and determining its rate each day; it is then for another week exposed to a temperature of 70°, and then to one of 85°; the next week it is returned to the temperature of 70°, and the last or fifth week it is exposed to the temperature of 55°, as at first. By means of general laws regulating the rates of chronometers it is now possible to determine what the rate will be at other temperatures than the three above mentioned, and knowing these, the navigator is able to apply the proper correction to his time-keeper so exactly that he need never mistake his position upon the ocean.
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Chronometer Tests . Nature 8, 150–151 (1873). https://doi.org/10.1038/008150a0
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DOI: https://doi.org/10.1038/008150a0