I 



. Chreiiomelerx. "lo 



tion, may be applied to define the straight parti of other Curves ? ; 

 that for instance, so very ingeniously and usefully produced, by 

 the combination of Levers vvliich direct the Piston -rod of Messr?* 

 Watt and Bolton's Steam-Engines ? 



IV. Mr. Adam Anderson in the last Number of the Edinburgh 

 Philosophical Journal, has investigated Rules, for calculating ilit 

 Dip, or visible depression of the Horizon at Sea : and (allowing 

 for Refraction, at the rate of '08 of the intercepted Arc of a 

 great Circle of the Earth) Jinds this dip in Miiiutes, to he very 

 nearly equal to the Square-root of the Height in Feet, of the Ob- 

 server's Eye above the Sea : he also mentions, as the usual ap- 

 proximate Rule for the converse of this in the practice of Levelling 

 on Land, the taking |rds of the Square of the Distance w (Eng- 

 lish) Miles, as equal to the correction in Height, for the Earth's 

 curvature. Quere, Is the last of these Rules consistent with the 

 first ? ; also, What are the most simple and consistent decimal 

 Multipliers for the Square-root in the first Rule and for Square 

 in the second Rule, to be sufficiently correct in practice ? ! ! and 

 What are the Heights and Corrections, to which such Rules will 

 apply, without sensible errors ? I am, yours, &c. 



London, April 9, 1821. An ENGINEER. 



CHRONOMETERS. 



'Change Alley, March 30, 1821. 



SfR, — In consequence of a report injurious to our reputation, 

 namely, that a Mr. Molyneux (and not ourselves) was the make! 

 of the chronometers which we had the honour of sending out 

 with Capt. Parry, and being apprehensive that this report may 

 have reached you, we trust to vour goodness to excuse our thus 

 troubling vou with the following statement, as we are particularly 

 desirous tliat you should be rightly informed on the subject. 



We beg positively to state, that Mr. Molyneux did not make 

 any jiart of those chronometers, nor were they ever in his pos- 

 session, neither did he ever see them. He has not been employed 

 by us for about these three years past until the present month. The 

 whole of the chronometrical parts were made in our house under 

 our direction, by workmen articled to us for the purpose of in- 

 structing them in that branch of the business; and the final cor- 

 rections and adjustments were completed by ourselves personally^ 

 in a method peculiarly our own, from a conviction that we had 

 discovered the causes of the material alterations which chrono- 

 meters frequently make in their rates. This method of correc- 

 tion was applied, to prevent that alteration, the particulars of 

 which we stated in a letter to Capt. Sabine at the time the chro- 

 nometers were delivered to him for trial. That we have suc- 

 ceeded in accomplishing this, is not only proved by the Polar 

 chronometers, but by others, we corrected at the same time, and 



Vol. 57. No.27G." ^pn7 1S2l. Rr which 



