154 PHILOSOPHICAL TRANSACTIONS. [aNNO I667. 



and some smaller parts ; and if carefully and curiously prosecuted, even to mi- 

 nutes too. But it will not be amiss to do it both by the sun and stars, for the 

 greater certainty. 



2. The dipping needle is to be used at least as often as the former experi- 

 ment is made. All that need be said of the manner is, that when the dipping 

 of the needle is to be examined, the circle in which it moves is to be hung per- 

 pendicular, and turned till it be just in the magnetical meridian, where it dips 

 the most, and the degree of its depression under the horizon is to be noted in a 

 table. See fig. 2, pi. 4. 



3. The chief particulars of the tides to be regarded are, the precise times of 

 the beginnings of the flood and ebb : which way currents run in all places, with 

 their times, changes, &c. The perpendicular heights and depths of the tide, and 

 lowest of the ebb : what day of the moon's age, and what times of the year, 

 the highest and lowest tides fall out. 



4. To sound the depth of the sea without a line. 



To perform this take a globe of fir or maple, or other light wood, as fig. 3, 

 pi. 4, let it be well secured by varnish, pitch, or otherwise, from imbibing 

 water ; then take a piece of lead or stone D, considerably heavier than will sink 

 the globe : Let there be a long wire staple B, in the ball A, and a springing 

 wire C, with a bended end F, and into the said staple press, with your fingers, 

 the springing wire on the bended end, and on it hang the weight D, by its 

 hook E ; and so let globe and all sink gently into the water, in the posture re- 

 presented in the said figure, to the bottom, where the weight D touching first 

 is thereby stopped ; but the ball, by the impetus it acquired in descending, being 

 carried downwards a little after the weight is stopped, suffers the springing wire 

 to fly back, and thereby sets itself at liberty to re-ascend. Then, by observing 

 the time of the ball's stay under water, either by a watch having minutes and 

 seconds, or by a good minute-glass, or best of all by aj)endulum vibrating 

 seconds, with the help of some tables, the depth of the sea will be known. 



In some of the trials already made with this instrument, the globe being of 

 maple wood, well covered with pitch to prevent its saturation, was 5-l-| inches 

 in diameter, and weighed 2^ pounds; the lead of 4-i- pounds weight, was of a 

 conical, but is now used of a globular figure, 1 1 inches long, with the sharper 

 end downwards, 1-^%- in diameter at the bottom. And in those experiments 

 made in the Thames, in the depth of 1 9 feet water, there passed between the 

 immersion and emersion of the globe six seconds ; and in the depth of ten feet 

 water, there passed 3^ seconds. From many of such experiments it will not 

 be difficult to find out a method to calculate what depth is to be concluded from 

 any time of the globe's stay under water : As for instance, if in the depth of 20 



