Occasionally, in these old curiosities, we trace anticipations of some of the scientific marvels of the present day. Thus, when the Grand Duke of Tuscany, in 1669, visited the Royal Society at Arundel House, he was shown “a clock, whose movements are derived from the vicinity of a loadstone; and it is so adjusted as to discover the distance of countries, at sea, by the longitude.” The analogy between this clock and the electrical clock of the present day is not a little remarkable. The Journal-book of the Society for 1669 contains many allusions to “Hook’s magnetic watch going slower or faster according to the greater or less distance of the loadstone, and so moving regularly in every posture.” On the occasion of the visit of illustrious strangers, this clock and Hook’s magnetic watches were always exhibited as great curiosities.[[4]]
[2]. Vulgar and Common Errors, book iv. chap. xii.
[3]. Time and Timekeepers. By Adam Thomson, 1842.
[4]. See Weld’s History of the Royal Society, vol. i. pp. 220, 221.
PERIODS OF REST.
The terrestrial day, and consequently the length of the cycle of light and darkness, being what it is, we find various parts of the constitution both of animals and vegetables which have a periodical character in their functions, corresponding to the diurnal succession of external conditions; and we find that the length of the period, as it exists in their constitution, coincides with the length of the natural day.
Man, in all nations and ages, takes his principal rest once in twenty-four hours; and the regularity of this practice seems most suitable to his health, though the duration of the time allotted to repose is extremely different in different cases. So far as we can judge, this period is of a length beneficial to the human frame, independently of the effect of external agents. In the voyages made into high northern latitudes, where the sun did not rise for three months, the crews of the ships were made to adhere, with the utmost punctuality, to the habit of retiring to rest at nine, and rising a quarter before six; and they enjoyed, under circumstances apparently the most trying, a state of salubrity quite remarkable. This shows that, according to the common constitution of such men, the cycle of twenty-fours is very commodious, though not imposed on them by external circumstances.
The succession of exertion and repose in the muscular system, of excited and dormant sensibility in the nervous, appears to be fundamentally connected with the muscular and nervous powers, whatever the nature of these may be. The necessity of these alternations is one of the measures of the intensity of these vital energies; and it would seem that we cannot, without assuming the human powers to be altered, suppose the intervals of tranquillity which they require to be much changed. This view agrees with the opinion of the most eminent physiologists. Thus, Cabanis notices the periodical and isochronous character of the desire of sleep, as well as of other appetites. He states that sleep is more easy and more salutary, in proportion as we go to rest and rise every day at the same hours; and observes that this periodicity seems to have a reference to the motions of the solar system.