TIDES. 



The following times ferve for coafts of coniiderable ex- 

 tent, and nearly for the places on thofe coafts ; w'a. Fin- 



mark, or N.N.W coaft of Lapland, l** 30" 



.Jutland ifles. 



o'^o"; Friefland coaft, y'' 30"" ; Zealand coaft, i'' 30" 

 Flanders coaft, o'' o™ ; Picardy and Normandy coafts, 

 jph jQm . Bifcay, Gallician, and Portugal coafts, 3'' o"' ; 

 Irifli weft coaft, 3'' o"" ; Irifli fouth coaft, 5'^ 15" ; Africa 

 ■weft coaft, 3'' o™ ; America weft coaft, 3'' o"" ; America 

 eaft coaft, 4'' 30™. 



The ufe of the preceding table is to find the time of 

 high-water at any of the places contained in it : for this 

 purpofe, find the time of the moon's fouthing on a given 

 day (fee Moon) ; and then add the time which the moon has 

 pafted the meridian on the full and change days, to make 

 high-water at that place ; and the fum fliews the time of 

 high-water on the given day. 



See on the fubjett of this article, Newton Princ. Math, 

 lib. iii. prop. 24. and De Syftem. Mundi, feft. 38-54. 

 Apud Opera Ed. Horfley, torn. iii. p. 25, &c. p. 203, 

 &c. Maclaurin's Account of fir I. Newton's Difcoveries, 

 book iv. ch 7. Fergufon's Aftron. ch. xvii. Robert- 

 fon's Navig. book vi. feft. vii. viii. ix. Young's Lec- 

 tures. 



TiDE-Z)/Vr/, the name of an inftrument contrived by Mr. 

 Fergufon, for exhibiting and determining the ftate of the 

 tides. It is reprefented in Plate IV. Dialling, Jig. 36. 

 and the external parts of it confift of i. An eight-fided 

 box, on the top of which, at the corners, are ihewn the 

 phaies of the moon at the oftants, quarters, and full. 

 Within thefe is a circle of 29^ equal parts, which are the 

 (lays of the moon's age reckoned from the fun at new 

 moon, round to the fun again. Within this circle is one of 

 twenty-four hours, divided into their halves and quarters. 

 2. A moving elliptical plate, painted blue, to fliew the 

 rifing of the tides under and oppofite to the moon, with the 

 v.ords high-iuater, tide-falling, low-water, tide-rijmg, marked 

 r.pon it. To one end of this plate is fixed the moon M by 

 the wire W, which goes along with it. 3. Above this 

 elliptical plate is a round one, with the points of the cora- 

 pafs upoa it, and alfo the names of above two hundred 



places in the large machine (but only thirty-two in the 

 figure, to avoid confufion ) fet over thofe points on which 

 the moon bears when flie raifes the tides to the greateft 

 heights at thefe places, twice in every lunar day ; and to 

 the north and fouth points of this plate are fixed two in- 

 dices I and K, which fliew the times of high-water, in the 

 hour-circle, at all thefe places. 4. Below the elliptical plate 

 are four fmall plates, two of which projeft out from below 

 its ends at new and full moon ; and fo, by lengthening the 

 eUipfe, ftiew the fpring-tides : the other two of thefe fmall 

 plates appear at low-water when the moon is in her quadra- 

 tures, or at the fides of the elliptic plate, to fliew the neap- 

 tides. When any two of thefe fmall plates appear, tlie 

 other two are hid ; and when the moon is in her oftants, 

 they all difappear. Within the box are a few wheels foi- 

 performing thefe motions by the handle H. Turn the 

 handle till the moon, M, comes to any given day of her age 

 in the circle of 29^ equal parts, and the moon's wire W will 

 interfeft the time of her coming to the meridian on that 

 day, in the hour-circle : the XII under the fun being mid- 

 day, and the oppofite XII mid-night: then looking for 

 the name of any given place on the round plate (which 

 makes 295 rotations, whilft the moon M makes only one 

 revolution from the fun to the fun again) turn the handle 

 till that place comes to the word high-water under the 

 moon, and the index which falls among the forenoon hours 

 will fliew the time of high-water at tliat place in the fore- 

 noon of the given day : then turn the plate half round, till 

 the fame place comes to the oppofite liigh-water mark, and 

 the index will fliew the time of high-water in the afternoon 

 at that place. And thus, as all the different places come 

 fuccefiively under and oppofite to the moon, the indices 

 fhew the times of high-water at them in both parts of the 

 day ; and when the fame places come to tlie low-water 

 marks, the indices fliew the times of low-water. For about 

 three days before and after tlie times of new and full moon, 

 the two fmall plates come out a little way from below the 

 high-water marks on the elliptical plate, to Ihew that the 

 tides rife ftill higher about thefe times : about the quarters, 

 the other two plates come out a little from under the low- 

 4 L 2 water 



