Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/423

 nesse of the Vessel, in its acquiring in several hours of the day several degrees of velocity, they are with very little difference acquired by all its parts; for as well the precedent as the subsequent, that is to say, both the Eastern and Western parts, do accelerate and retard almost in the same manner; and withal making that alteration by little and little, and not by giving the motion of the conteining Vessel a sudden check, and retardment, or a sudden and great impulse or acceleration; both it and all its parts, come to be gently and equally impressed with the same degrees of velocity; from which uniformity it followeth, that also the conteined water with but small resistance and opposition, receiveth the same impressions, and by consequence doth give but very obscure signes of its rising or falling, or of its running towards one part or another. The which effect is likewise manifestly to be seen in the little artificial Vessels, wherein the contained water doth receive the self same impressions of velocity; when ever the acceleration and retardation is made by gentle and uniform proportion. But in the Straights and Bays that for a great length distend themselves from East to West, the acceleration and retardation is more notable and more uneven, for that one of its extreams shall be much retarded in motion, and the other shall at the same time move very swiftly: The reciprocal libration or levelling of the water proceeding from the impetus that it had conceived from the motion of its container. The which libration, as hath been noted, hath its undulations very frequent in small Vessels; from whence ensues, that though there do reside in the Terrestrial motions the cause of conferring on the waters a motion onely from twelve hours to twelve hours, for that the motion of the conteining Vessels do extreamly accelerate and extreamly retard but once every day, and no more; yet neverthelesse this same second cause depending on the gravity of the water which striveth to reduce it self to equilibration, and that according to the shortnesse of the Vessel hath its reciprocations of one, two, three, or more hours, this intermixing with the first, which also it self in small Vessels is very little, it becommeth upon the whole altogether insensible. For the primary cause, which hath the periods of twelve hours, having not made and end of imprinting the precedent commotion, it is overtaken and opposed by the other second, dependant on the waters own weight, which according to the brevity and profundity of the Vessel, hath the time of its undulations of one, two, three, four, or more hours; and this contending with the other former one, disturbeth and removeth it, not permitting it to come to the height, no nor to the half of its motion; and by this contestation the evidence of the ebbing and