128 PHILOSOPHICAL TRANSACTIONS. [aNNO 1726. 



fixed another plate, which was graduated in such manner, that by the half- 

 minute glass it would tell what the vessel ran in that space of time, &c. 



On the third dial were 3 circles: the first was so divided as to show when the 

 ship had run 6o leagues; the second, when the ship had run the same distance 

 in miles; and on the third was marked 120 knots; so that, computing each 

 knot at 50 feet, the circumference was 6000 feel, the standard of an English 

 maritime mile, or the 6oth part of a degree on the equator, in running which 

 length, the instrument has just 6oo revolutions; to which distance a little bell 

 strikes, to give notice to the man at the helm, of the distance sailed in that 

 time. 



Besides the several circles on this dial, were also two plates on each side, 

 having two circles, one divided into 100 leagues, and the other into 300 miles; 

 so that, without hearing the bell strike to every mile or league, one might at 

 any time see by them, what number of miles or leagues the ship had run, from 

 the time she had left her port. As to the materials within the dial, there is 

 little more than common clock-work. 



As by this machine Mr. S. undertakes to correct the errors of the log, he 

 states the particulars of a comparison between that instrument and his inven- 

 tion. He remarks on the inaccuracy of estimating the time by the half-minute 

 or quarter-minute glass; on the uncertainty of the log floating quite upright, 

 and dragging, as well as in heaving it over and veering out the line; then the 

 uncertainty from the line itself, being at times longer or shorter, from drought 

 or moisture: also the uncertainty arising from the changeable velocity of the 

 ship, faster or slower, in the intervals between the times of heaving the log, 

 by the variable state of the winds, &c. From all which irregularities, Mr. S. 

 asserts his instrument is quite free and exempt. He concludes with subjoining 

 the testimonials of its accuracy and usefulness by several experienced seamen, 

 who had made trial of his machine. 



END OF VOLUME THIRTY-THIRD OF THE ORIGINAL. 



De Salibus AkaVmo-Jixis, Auclore C. Newman, Chem. Prof. Reg. Berolin, 

 R. S. S. N° 392, p. I. Fol. XXXIF. 



In this, and the subsequent dissertation, the author treats at great length of 

 the production, properties, and uses of fixed alkaline salts; but as the fullest 



